Pathway to Japanese Literature

Detective Homura Appears

Lately, people hadn’t been hearing much about the activities of that young detective Homura Sōroku, and suspicions arose about what had become of the Master—until it was learned that he’d been occupied with a troublesome case commissioned by certain quarters.
Recently, he seemed to have been staying continuously at his own office.
The work from certain quarters had reached a temporary pause, so he said arrangements had been made for him to take a break from that work for the time being while recuperating.

I actually met Homura Sōroku at a certain place yesterday for the first time in ages.

He was wrapped in a plain suit that accentuated his characteristic tall frame, yet somehow appeared to have aged considerably.
His complexion had grown deeply sunburnt, the sickly pallor that usually hinted at his weak stomach now completely vanished.
Having swapped his tinted glasses for thick-framed ones, he looked thoroughly like a doddering old man from every angle.
When I teased him about this transformation, he twisted his trademark large mouth into a tight, sly grin,

“Heh heh heh, these days I can’t go without this look.
Whether I’m prowling city streets or poking around the countryside, I’ve got to look like some middle-aged nobody you’d pass without a second glance—otherwise the job’s impossible.
I need to move among those rats without them sniffing out who I really am, all while watching their every twitch.
If I still dressed in those flashy getups tailored to my old tastes, every fish in the pond would dart for cover.”

He delivered this defense of his drab appearance with practiced ease.

So I pressed him to tell me about any particularly interesting cases he’d handled lately, but Homura flatly rejected my request.

“There are certainly intriguing espionage cases, but if I were to publicly reveal how I cracked them, all the important fish I’m about to catch would swim away.”

And he repeated the same thing.

Are the fish that dart about in such cases really that cunning?
To that question, Homura Sōroku—

“The adversaries that appear in such cases are all highly intelligent individuals.”
“So if we let our guard down even slightly, they’ll instantly turn it against us.”
“This is exactly what it means to leave no room for carelessness or lapses in vigilance.”
“And since they’re all risking their lives, it’s unbelievably dangerous.”
“Moreover, their numbers are vast, their organization is exceptionally robust, and they wield every conceivable resource.”
“Facing them with our small numbers like this—it’s truly grueling.”

“Shouldn’t there be some harmless story you could share from around that time?”

As I promptly prompted him, he lit a fresh cigarette and—
“Hmm, I suppose I could tell you just one story.
This is a tale of failure I brought upon myself eight or nine years ago.
I think it will serve as an example of how those tenacious opponents go about devising their schemes.
For my part, I had never before encountered a case that made me rack my brains this much.
I taxed my brain so hard I thought my cells might disintegrate—no, utterly exhausted my mind. And looking back later, it was infuriating beyond measure—a ridiculous case of wasted energy where I alone spun round and round like a top, completely fooled.”

Homura said this and twisted his large lips tightly in a manner that suggested unbearable resentment.

When I insisted on hearing it, he—

“Alright, I’ll tell it, but no matter how foolish this case may seem, as I mentioned earlier, it’s the one that wore me down to the bone more than any I’ve handled. So you must listen quietly through to the end—with deepest sympathy—while carefully pondering each detail as you go. Otherwise this simply won’t do.”

And so, unlike usual, he imposed upon me the fervor of a listener.

Of course I vowed to listen with utmost attentiveness, but looking back now, it seems Homura had tasted a gallingly bitter ordeal in that case.

And so begins Homura's tale.

The Secret Man

I believe those subsequent few years likely marked the period when the most diverse array of intelligence agencies operated within our country.
Alongside those handling international relations, there existed profit-driven specialists, information communication experts, economic affairs operatives - spies of considerable variety were actively engaged.
Occasionally there was even infighting among comrades, creating rather intriguing situations.

The two things we must never permit enemy spies to accomplish were their learning our secrets and their relaying this information to their headquarters. Among these, communications falling under the latter category demanded vigilance so watertight not a drop could leak through.

Discovering all secret communication agencies and seizing them from spies' hands had become an urgent priority.
Fortunately, our nation's communication industry being either monopolized or strictly regulated by government authorities made oversight relatively straightforward, while the surveillance technology these authorities possessed could promptly detect even when secret transmitters persistently sent out Morse code signals—both proving advantageous.
At that time, the number of secret communication agencies exposed or discovered through such means grew exceptionally large.

The state-of-the-art shortwave radio equipped at Homura Sōroku’s office also underwent inspection by the authorities and naturally came under discussion for confiscation. However, as he had already been assigned certain work at that time—and since the device was deemed necessary for those duties—it fortunately escaped seizure.
At that time, Homura had not yet recognized how valuable this shortwave radio had become by then, but according to accounts he later heard, among civilian devices of that era, there were almost none apart from Homura’s own that avoided confiscation.
At that time, Homura had not yet recognized the gravity of such circumstances.
Of course, had he heard such an explanation from someone, he would have understood and been on guard; but in fact, no explanation was provided.

Now one day, a call came in to Homura's office.
When an assistant named Ōtsuji answered and asked for the caller’s name, the voice inquired, "Are you Mr. Homura?"
When Assistant Ōtsuji responded, "I am not my employer, Homura," the caller demanded to speak to Mr. Homura directly yet stubbornly refused to identify himself.
Ōtsuji relayed this to Homura, but this manner of phone call—a tactic often used by clients wishing to conceal their identity—wasn’t particularly remarkable.

When Homura took over the call, the caller once again meticulously confirmed it was indeed Homura before—

“—Actually, we’re from the Ministry of Home Affairs, and we wish to secretly enlist your assistance.”

—and finally revealed his identity.

Though this marked his first negotiation with such a government office, Homura made clear his provisional willingness to assist given its official nature and inquired about the details of the requested case.

Then the man said,

“No, naturally this isn’t something we can discuss over the phone—I need to meet you in person.”

“Then when shall I come to see you?” Homura asked.

“I would prefer it to be as soon as possible,” came the reply. “However, were you to come here—given how various individuals are constantly coming and going—it would draw undue attention. Let us meet elsewhere instead. In that case, proceed as follows.”

With this, the official who had introduced himself as Mr. Kimura instructed Homura to stand at a designated spot within Hibiya Park thirty minutes hence. He explained he would pass by in an automobile bearing a specific license number, requested Homura board the vehicle there, and stated he would handle all subsequent arrangements.

Homura acknowledged his understanding and hung up.

After briefly informing Assistant Ōtsuji about the phone call—prefacing that he would depart immediately—Homura issued instructions: Ōtsuji was to conceal himself in the park with a car to confirm where Homura would be taken, execute discreet surveillance, return to the office upon identifying the destination, and if no call arrived from Homura within one hour, rush to intervene immediately. With these orders given, Homura left the office.
For even if government offices themselves held no particular suspicion, there was always the chance that rogues might pose as officials on official business and catch them off guard.

Homura made thorough preparations and, as instructed by Mr. Kimura, stood at the designated spot in Hibiya Park thirty minutes later.

Five minutes after that, a car passed by—a large sedan in form but of an extremely antiquated model.
It was immediately recognizable as a government vehicle at first glance.
A small flag bearing the government office’s emblem stood erected atop the radiator.

Ah, this must be it.

Just as this thought crossed his mind, the car came to an abrupt halt before Homura, and the mustached gentleman around forty inside leaned his face toward him,

“I’m Kimura.”
“Please, get in.”

he called out in a soft voice.

Homura simply became an occupant of the vehicle.

And he passed through the gate of a certain traditional restaurant in Tsukiji under Mr. Kimura's guidance.
The time was exactly 3:17 p.m.

Cipher Key

“Ah, I must apologize for bringing you to such an unseemly location—”
“But without these precautions, news of our ministry having enlisted your help for this grave matter would spread everywhere.”

Having exchanged initial greetings, Intelligence Division official Mr. Kimura Seijirō immediately turned to business.

“—This concerns an urgent investigation vital to the government’s interests. Naturally, you must maintain absolute confidentiality.”
“You may already know this—there exists a powerful anti-government group currently intensifying its activities.”
“This secret organization’s headquarters appears to be based in Shanghai or thereabouts. Daily communications containing intelligence and directives arrive from this base—transmitted via a covert wireless telegraph system employing encryption.”
“Consequently, even if one attempted interception with standard receivers, the covert transmission protocols render ordinary equipment ineffective.”
“Furthermore, since the code itself is encrypted, obtaining a copy would prove meaningless without deciphering capability.”
“Thus they’ve established dual-layer security through these means.”
“You follow my meaning?”

Homura silently nodded.
I'm already well aware of that.

Mr. Kimura continued speaking,

“Since this is confidential, I must ask you to handle it without error.”
“Now, the problem lies in the cipher decryption key.”
“We simply can’t determine it.”
Tilting his head, he added: “The ciphertexts they send are six-digit numerical formulas.”
“In other words, six-digit numbers like 123456 indicate letters such as A or B.”
“However, those six-digit numbers remain indecipherable no matter how much you attempt to solve them as they are.”
“This cipher method employs another six-digit number as the key—they’ve added it to every digit.”
“For example, if the key number were 330022, this would be added to every number in the ciphertext.”
“Therefore, even if A is represented by 123456, they transmit not 123456 itself but the sum—453478 after adding 330022.”
“Thus anyone intercepting 453478 mid-transmission couldn’t possibly deduce the true cipher 123456.”
“Now this key number proves crucial—forgive me for ‘preaching to the choir’—but here’s the complication: it changes effortlessly every month.”
“If this month’s key were 330022, come the first of next month it would abruptly shift to something like 787878.”
“This leaves our decryption team utterly distraught.”

With that, Mr. Kimura drank his tea.

The restaurant staff member left after placing tea and sweets before the two.
They had been instructed not to come until summoned from this side.

“Our decryption team comprises skilled members, but extracting the key number from six-digit cipher numbers remains quite a challenge."
“Just when they think they’ve finally found it after all that struggle, it’s already the end of the month, and the next one arrives right away.”
“When that happens, a new key number comes in—so starting from the first day onward, their cipher becomes completely unsolvable.”
“They have to start studying the key number all over again.”
"For me as well, the decryption staff’s hardships are always a heavy burden on my heart."

With that, Mr. Kimura let out a deep sigh.

Homura continued nodding silently.
The content of Mr. Kimura’s cipher explanation perfectly matched his own knowledge.

“Now regarding this key number—if we could successfully discover it before the month changes, nothing would be more beneficial for us.”

“I see.”

“You understand how it is, yes?
“We’ve spent considerable time investigating how and when this cipher key number gets transmitted—only very recently have we finally begun grasping its mechanism.”

“Hohō, that’s delightful.”

Homura finally leaned forward.

"It's truly a joy profound enough to make tears well up."
"We initially believed the cipher key would come through wireless transmissions too, but that proved incorrect."
"The secret society's headquarters have executed their preparations with meticulous thoroughness."

"Ah."

"Why do you suppose they're notifying this branch office about the key number?"

"Well—"

"To speak frankly, even we haven't fully grasped that yet."

“Well then—”

“Ah, but we’ve finally grasped a valuable lead.”
“Please take a look.”
“Here it is.”

With that, what Mr. Kimura brought out before Homura’s eyes was a black briefcase.

What had emerged from the briefcase—what in the world could it be?
It was a roughly B4-sized board, with a large golden pen nib affixed to its surface.
It appeared to be an advertisement signboard for pen nibs.
It bore the name of a certain famous British pen nib manufacturing company.
And so that this signboard could be hung, metal fittings had been attached.

“This is quite intriguing. However, I don’t understand how this relates to the cipher key number.”

Homura shook his head.

“I will explain immediately,” said Mr. Kimura. “There exists a complete explanation. Observe this.”

With that, he extracted a flashlight-like slender object from his briefcase and positioned it against the pen nib signboard’s reverse side.

“Now—when I press this ultraviolet lamp’s switch and direct its light onto the back panel,” he continued, “then something truly fascinating will manifest upon this apparently blank board.”

The slender flashlight-like object Mr. Kimura held was indeed an ultraviolet lamp.
As Homura watched in fascination, the switch clicked on—the back panel suddenly glowed blue.
When he looked, it had formed into characters—hadn't it—
“①x=□□□□□□=74□×?”

“②: Teito Department Store Western Liquor Section’s ‘Scotch Whisky’ at Ginza 4-chome, Tokyo City
The Scotch Whisky advertisement’s back side.
‘On the nose tip of the person wearing a red coat there is a star mark.’”

And written there was something truly shocking.

Transportation Expenses: ¥10,000

Homura Sōroku parted ways with Official Kimura and finally launched into action.

The □□□□□□ in x=□□□□□□ written on the back of the pen nib signboard was indeed the cipher key number they sought. However, without clearly writing what number it was—74□×?—they had evasively written it in this peculiar manner. And it was written in a way that designated this as ① while instructing them to search for ② thereafter. Truly a mysterious pen nib signboard.

Homura fired a volley of questions about how Official Kimura had obtained this, but the official refused to explain. And then he said:

“If I were to explain that, it would compromise our government office’s vital intelligence network—I must ask your forbearance.”
“However, I can assert this bears full credibility.”
“There remains no doubt this □□□□□□ constitutes next month’s cipher key number, yet the essential digits themselves are missing.”
“This compels us to proceed to location ②—specifically locating the Scotch Whisky advertisement in Ginza’s Teito Department Store Western Liquor Section—and examining its reverse side for deductions. Yet I desire to entrust this task to you.”
“Though not entirely beyond our own capabilities, as I have reiterated, such direct involvement would instantly alert their faction.”
“By engaging your services, we achieve both skillful camouflage and—I believe—execution far surpassing our crude methods.”
“I earnestly entreat you to weigh these circumstances and initiate operations without delay.”
“Absolute confidentiality must be maintained.”
“Additionally—though it pains me to impose—today being the 26th leaves but five days until next month.”
“Hence I must insist you embark on this investigation posthaste.”
“Furthermore, employ every conceivable means to expedite completion by even a single hour.”
“Should we tarry, catastrophic losses await the government—and need I add, you must exercise utmost vigilance regarding personal security.”

With that, Official Kimura handed Homura a bundle of ¥10,000 banknotes as transportation expenses.
Adding that Homura should request funds if needed, he handed over a business card indicating a secret liaison office at an unspecified location in the city.
The place was disguised as an ordinary private residence but contained a long-distance telephone, telegraphic codes, and even detailed transfer numbers recorded.

Homura Sōroku felt an extraordinary level of intense excitement from this meeting with Official Kimura.
He was a formidable opponent indeed.
He would locate the cipher key for next month that had been sent to him—no matter what dangers he had to risk—within these five days.
He was fully aware that this was an extremely difficult task.
He had never heard of any existing cipher that presented something mathematical like this.
It was clear this would be grueling work.

“Alright.”
“No matter what it takes—I won’t leave this six-digit cipher key unsolved!”

Homura exited the traditional restaurant and immediately rushed into a public telephone booth, summoning Assistant Ōtsuji to the receiver.
When it came to such critical matters, he found it difficult to fully explain even to Ōtsuji, but conveyed the general idea appropriately and requested that his assistant properly manage the office during his upcoming five-day absence as previously instructed.

“Master, I’m worried you’re not taking me along.”
“However, if I cannot accompany you, there’s nothing to be done. But please, take utmost care of yourself.”

Assistant Ōtsuji remained deeply concerned about Homura’s well-being.

And thus Homura's investigation finally began in earnest.
It was a completely solo endeavor.

His brain and physical strength were his sole capital.

①x=□□□□□□=74□×?

Now came the challenge of solving this—the enigma of this peculiar cipher.

At any rate, his next objective was ②.
The location specified was the Western Liquor Section of Ginza's Teito Department Store.

He immediately made his way to the Western Liquor Section’s sales area on basement level one.

Sauntering through the Western liquor section while pretending to browse, he finally discovered the Scotch Whisky pictorial signboard among the shelves lined with liquor bottles.
Sure enough, it depicted an Englishman from the 1700s clad in a red coat.
When he approached and looked, the familiar special one-star symbol had been inscribed on the tip of its nose.

“May I help you?”

A cocky-looking store clerk addressed Homura.
His demeanor practically shouted, "A pauper like you has no business here."

“Ah, that thing there.”
“I need to collect cocktail ingredients.”
“Since I want to inspect that shelf over there—lend me the ladder.”

Homura had them bring a ladder, then strode right up it.
And he continued haphazardly selecting one expensive Western liquor bottle after another.

The store clerk’s attitude changed so abruptly it bordered on comical.
When Homura mentioned a Western liquor that wasn’t there, the clerk said, “Since it’s in the warehouse, I’ll bring it right away,” and darted off toward the back.
This was precisely Homura’s moment. Remaining atop the ladder, he quietly detached the Scotch Whisky pictorial advertisement from the side concealed by his body and pressed the ultraviolet lamp provided by Official Kimura against its reverse surface.

“Ah! So that’s it!”

Even having anticipated this outcome, Homura couldn’t fully suppress his astonishment at discovering the mystery of the evolving secret numbers—written in invisible ink—progressing exactly as predicted.
The characters inscribed there were those shown above.

[First Diagram]

②

8

＿＿＿＿＿＿＿

74□)□□□□□□

□□□2

―――――

③ハ Tokyo Shinjuku Oiwake “Hamada”
Inside the billiard hall: World Billiards Player "Mr. Jonason"
Noposutā no ura.

Cufflinks bear star symbol.

Unfinished division

Inside the yen taxi, Homura peered intently into his notebook while scratching his head.

According to the records of ② gathered at Teito Department Store, the six-digit number in question had indeed assumed the form of an extraordinary division problem.
Dividing this enigmatic number by 74□—with its quotient’s first digit made to be 8—then multiplying it again by 74□ yielded a value ending in □□□2.

This is truly an astonishing method for concealing a cipher.

Homura remained steeped in prolonged astonishment.

The code numbers couldn’t be deciphered at a single location—one had to pursue second and third sites in sequence to unravel them. Moreover, the sought number took the form of a dividend, structured such that those lacking intellect could never hope to decipher it outright. This setup ensured that unless one painstakingly deduced each digit concealed within those squares, the sought number would never reveal itself.

“This has turned into a sixfold puzzle.”

He thought this through but knew he had to devise an answer swiftly—there was no time left to waste.
The crisis loomed ever closer.
"Very well—I'll think this through properly," he resolved.

Homura stared intently at the notebook he had copied. After staring at it for some time, he grasped a single hint.

"Ah! Indeed—it really does help to think things through."
"It’s coming together bit by bit, isn’t it?"

How had he approached this?

Multiplying 74□ by 8 results in □□□2.
Cases where multiplying by 8 like this yields a 2 in the ones place aren’t all that many.—He added notations like those above to his notebook.

[Second Diagram]

②

8←Ha

＿＿＿＿＿＿＿

74A)BCDEFG

↑↑ HIJ2

Iro ↑

Ni

The letters A, B, C, etc., represented digits whose exact values remained undetermined.
Iro, Ha, and others were digits that had already been determined as 7 and 4.

Therefore, the current focus was on determining A.
Now, after trying various approaches, it became clear that A could yield two possible values.
Namely, there were two possibilities: A=4 and A=9.

If A=4, then multiplying 744 by 8 yielded an answer of 5952.
If A=9, then multiplying 749 by 8 resulted in an answer of 5992.
Both had 2 in the ones place.
This was the first discovery.

Encouraged by this breakthrough and persisting with his calculations, Homura discovered that two of the previously inscrutable numbers could now be definitively determined—a revelation that filled him with such joy he nearly leapt from his seat.

Which squares' numbers would those be?

To state the conclusion first: H=5 and I=9 were determined.
For when A=4 as previously stated yields 5952, and A=9 yields 5992—comparing these two reveals that both share 59 in the thousands and hundreds places.
Therefore, naturally H=5 and I=9 had to hold true.

“Ah! Indeed—this is an intriguing answer.”

As Homura exclaimed under his breath, the yen taxi carrying him slowed toward Shinjuku Oiwake’s paved road, the driver glancing back through the rearview mirror—

“Will this spot do, sir?”

he asked.

Homura stowed the crucial notebook in his pocket and stepped down onto the pavement.

Now he was about to enter Hamada Billiard Hall.
Would he manage to locate that particular poster?
Would the path ahead bring clear skies, cloudy skies, or a storm?

As it was still early evening, all seven billiard tables at Hamada Billiard Hall were packed with students and office workers.
Homura, having no other choice, sipped the tea brought by the game attendant while waiting for a table to open up—or at least maintaining that pretense—and used the opportunity to scrutinize the posters hanging throughout the hall.

"It’s gone! No matter how much I look—nowhere to be found."
"Strange."

Homura was disappointed.
The poster of Mr. Jonathan that should have been there was nowhere to be seen.
If that wasn’t there, this hard-won detective case would meet its end here.
That would spell disaster.
He crossed his arms and devised his next stratagem.

After a moment, a smile suddenly appeared at the corners of his mouth.
He stood up and walked over to the Madam whose attire made her look like she lived next to a towel steamer.

“Say, Madam. You must’ve received Jonathan’s poster by now. Take that out. It’ll look proper hung on the wall.”

“The Jonathan poster—ah, that one! It’s still been left rolled up in storage. What do we have here?”

With that, the Madam retrieved the spiral-rolled poster from the cabinet. When unrolled, Jonathan’s signature stood printed there plain as day. Homura’s sixth sense had pierced true.

Homura pasted the poster on the wall, then told the game attendant he’d go downstairs for some tea since the tables didn’t seem likely to open up anytime soon, and stepped outside.

As soon as he stepped outside, he hailed a yen taxi and became its passenger.

“Where to, sir?”

“Yeah, Tokyo Station. I’m short on time—step on it.”

Tower of London

Homura was swaying within a second-class carriage while descending the Tōkaidō Line.

He barely managed to board the Okayama-bound train departing Tokyo Station at precisely six p.m.
The train now left Yokohama Station’s platform and was steadily gaining speed toward its next stop at Ōfuna.

The passenger compartment stood starkly empty.
Given the hour, few passengers rode in the second-class carriage of this slow train.
He reached into his pocket and carefully unfolded the crucial notebook.

There lay a note marked with the symbol ③—when had it been written?—following the same format as those before.

[Figure 3]

③

8

＿＿＿＿＿＿＿

74□)□□□□□□

□□□2

―――――

□9□□

④ Ha: Front of Numazu Station, Kikuya Dining Hall's "London". The back of the mirror bearing the photographic print of the tower. On the third window from the tower's top was a star mark.

This was a transcription of the characters Homura had swiftly deciphered by shining an ultraviolet lamp on the back of that world-renowned billiards player Jonathan’s poster stored away at the Shinjuku Oiwake Hamada Billiard Hall.
According to this, the division had become three segments, with one additional segment.

Homura became frantic and directed his attention to this month-short division problem.
A four-digit number—□9□□—had been added to the third segment, and he was certain this would allow him to make fresh inferences about the numbers within the enigmatic boxes.

He revised his notebook.

[Figure 4]

③

8←Ha

＿＿＿＿＿＿＿

74A)BCDEFG

↑↑ HIJ2←Ni

Iro ―――――

K9LM

↑

Ho

The first thing that became clear was that D had to be smaller than J.
As previously determined through deduction—since J could only be 5 or 9—the appearance of 9 in position Ho below necessitated this relationship; D above absolutely had to be numerically inferior to J below for this configuration to hold true.

This meant D required borrowing 1 from its upper digit C before subtracting J.

But this created an impossibility regarding C’s value—it couldn’t be zero.
If C were zero, transferring 1 to D would leave 9 remaining above I’s position below—yet since I itself was 9, subtracting these identical values would force K to become zero through 9－9＝0.
However, K’s non-zero status was explicitly indicated by its framed box in the diagram.
Thus C’s exclusion from being zero became irrefutable.

This conclusively determined that B=6.
Because below B lay H=5, and there were no digits beneath that.
Moreover, since C was not zero—even if it were 9, it would leave 8 after giving 1 to D—for I (i.e., 9) to be subtracted, B had to be 6 with no other possible digit.

When he examined D more closely, he found that with a divisor of 744, D became 4; with 749, D became 8.

However, if E were 1 or zero—values less than 2—it would result in another digit above, but such cases had to be considered rare for now—.

He still couldn’t clarify the rest.
Homura closed the notebook and turned his gaze to the rural scenery streaming swiftly past the train window.
The fields were lush green everywhere, and as he marveled at how utterly peaceful they looked, drowsiness overtook him and he fell fast asleep.

He had no idea how long he'd slept.
The train jolted with a metallic clatter, jerking him awake.
At that precise instant, the locomotive slowed its speed and glided into station grounds blazing with electric lights.
Checking the station sign revealed Numazu.
The digital clock read exactly 8:55 PM.

He abandoned the train and exited the station.

He was terribly hungry.
There had been a reason he refrained from eating aboard.
It wasn’t some random idea.
If he needed to investigate Kikuya Dining Hall before the station per that treasure hunt-like cipher guide, keeping his stomach empty had been more practical.

Kikuya Dining Hall had a large signboard out front, so he recognized it immediately.

“Sis.”
“I’m completely starved.”
“Can you hurry up and fix me a meal?”
“Let’s see… Fried shrimp, sashimi, rolled omelet, miso soup, rice curry, and then…”

The waitress giggled.
It was because the order was excessively large.

Taking that as his cue, Homura found himself growing more at ease with the waitress.

“Well, well! This has a beautiful bridge, doesn’t it?”

With that, Homura approached the wall.

“It’s a photo of the Tower of London.”
“They say many people were killed there long ago.”
“And princes were among them too, you know.”

“Huh, you’re quite knowledgeable. It’s so beautiful you’d never guess it was such a dreadful place.”
“I see.”

Just then, a voice called out from inside, summoning the waitress.
It seemed the meal had finally arrived.
Homura effortlessly flipped over the Tower of London and retrieved the secret characters written in ultraviolet paint on the mirror’s reverse side.

Just as he finished transcribing it into his notebook, the waitress arrived carrying a tray with a steaming rolled omelet.
Homura returned to the table with an innocent look on his face.

While devouring the bland dishes being brought out one after another, Homura kept glancing repeatedly at the timetable pasted on the wall.

"There was no choice but to board the 10:25 Kobe-bound express."

He was thinking about his next journey.
The destination was Osaka.
He felt vaguely uneasy about drifting ever westward, putting more distance between himself and Tokyo with each passing moment.
He interpreted this unease as the homesickness of one who leaves their native land, despising his own mental weakness.

When he finished eating and checked his watch, finding he still had nearly a full hour before boarding the train, he assumed the posture of someone cooling off by the window while in fact mentally mapping out developments in the new cipher retrieved from that mirror’s reverse side.

His notebook contained what was written as shown in Diagram V.

[Diagram V]

④

8□

＿＿＿＿＿＿＿

74□)□□□□□□

□□□2

―――――

□9□□

□74□

⑤ハ: Posted within Osaka City’s Shinsekai “Ashibe” Theater – “Robin Hood”
Lower right corner of the poster.
Star mark present.

Looking at this, the second digit of the answer appears, but since it's enclosed in a frame, it's impossible to tell what number it is.
The fact that only two characters—□74□—out of the four digits in the fourth row had been deciphered was a significant lead.

Homura organized this, inserting the numbers he had deciphered so far and adding new symbols into the fresh frames.
It was as shown in the separate diagram.

(Diagram VI)

[Diagram VI]

④

ハ

↓

8X

＿＿＿＿＿＿＿

74A)6CDEFG

↑↑ 59J2←ニ

Iro ↑↑

HI

―――――

K9LM

↑

Ho

N74P

↑↑

Heto

Homura continued working through possible solutions.

Since Heto showed 74, he needed to focus his analysis there.
The second digit of the answer was X - multiplying this X by the divisor 74A would yield N74P.

Now, for Heto - specifically its leading 7 - to appear in that position, he deduced X must correlate directly with the 74 portion of the divisor.

When he substituted X with values from 0 through 9 and examined them, X's value was narrowed down to one of two possibilities.
X=5?
Or 9?
To elaborate—if X were 5, multiplying it by the divisor's first two digits 74 would yield 370, producing a 7 in the Heto position.
If X were 9, the product would become 666 initially showing a 6, but when accounting for the A×X term, this would adjust the 666 to something like 67?, ultimately resulting in a 7 there as well.

In any case, through this process, X had been narrowed down to either 5 or 9.

Proceeding further to examine cases where A in divisor 74A was 4 and 9, he arrived at the following.

When X was 5 with 744, the result was 3720.
This didn’t match □74□, so the assumption proved invalid.

Next, trying X=9 with 744 yielded 6696, which also failed to fit the □74□ pattern.

This time, setting A to 9 and testing X=5 against 749 produced 3745—a perfect match for □74□.

Another test assuming X=9 with 749 also resulted in 6741, matching the pattern.

Thus, 744 was rejected and 749 became the correct fit.

Therefore, he concluded that A=9.

As for X, it was still unclear whether it was 5 or 9.

Once A was fixed at 9, HIJ2 could be neatly calculated to 5992.
H and I had been known from before, but with this, J=9 was determined.

Now it was just a matter of whether N was 3 or 6 and P was 5 or 1—but that was all.

Having come this far in his reasoning, Homura finally felt as if he had set down one heavy burden.
He couldn't bear his impatience to reach Osaka quickly and crack this cipher.

Distress Signal

Homura spent the night on the train.
Yet by 6:38 the next morning, the train pulled into Osaka Station.

Perhaps from mental fatigue, his head ached.
Enduring it, he took his first step into the streets of Osaka.

The Shinsekai district near Tennōji was Osaka’s premier entertainment zone.
There stood Tsūtenkaku, modeled after Paris's Eiffel Tower, beneath which movie theaters, restaurants, inns, and radium hot springs were densely packed together.

Because Homura was already straining every nerve, he raced by car to this Shinsekai without even washing his face or eating a meal.

Ashibe Theater was located right next to Tsūtenkaku.
However, it was still too early in the morning; the front doors were shut tight, leaving no way to peer inside.
When he asked a passing woman, he learned that he would still have to wait about three more hours.
He finally found time to calmly wash his face and eat breakfast.
When he saw the theater had begun selling tickets, Homura was the first to enter the auditorium.
And the long-awaited fifth notebook was successfully obtained.
It was as shown separately.
(Figure 7)

[Figure 7]

⑤

8□

＿＿＿＿＿＿＿

74□)□□□□□□

□□□2

―――――

□9□□

□74□

―――――

□□4□

⑥ The dial of the "Orgel" clock kept at the Toyama City Public Hall office.
The trademark location bears a star symbol.

□□4□ and the fifth-stage four-digit number emerged.
He assigned the symbol QR4S to this.

Homura, who had investigated expecting matters to be largely settled at this stage, found himself facing profound disappointment.
There had been no new determinations at all.
Just as F had been M and G was S, none of it meant anything without knowing what numbers they represented.

"I have to get to Toyama as soon as possible."

In the Ashibe Theater lounge, Homura let out a single large yawn.

Apparently, Toyama appeared to be the final destination now. Everything would be decided there.

Steadying his unsteady body, Homura called Japan Air Transport.

"Is there one seat available on the Toyama-bound passenger plane?"
"Today, of course."

A reply came through—there was availability, they said.
There, he requested the ticket and registered his name.
When he asked about the departure time, they said it was 11:10 a.m.
There was about an hour and a half left.

As Homura stepped out of the public telephone booth, he suddenly craved a drink.

He didn't have much time left, but being this dizzy wouldn't do.
Especially since he now faced an air journey.
He absolutely needed to knock one back.
Having thought this, he scoured Shinsekai round and round, searching for a place where he could drink.

He later learned this alley was called Gunkan Yokocho, where rows of lively oden shops—a rare sight in Tokyo—stood side by side.
Five or six young women in bright red kimonos sat behind pots of simmering oden, vigorously plucking their shamisens.
Even though there were no customers, they sang bawdy songs at the top of their lungs.
Though he thought oden seemed ill-suited for this heat, the carefree shamisen strains struck a chord with Homura, and he entered to request sake.

What followed thereafter were matters I would rather not document for Homura's honor.
In any case, by 10 PM that night, he stumbled into Osaka Station.

"I'm going to Toyama, I tell you."
"One ticket here."

He clung to the ticket counter window, his tongue still thick and slurred.
He seemed to have been drinking heavily.
The plane—he’d missed boarding that long ago.

“Hey Yamashita-kun. Y-you… you ran off somewhere!”

He was calling out names of people even he himself had no memory of.

He finally managed to board the 10:18 PM train.
And no sooner had he burrowed into the berth than he began emitting python-like snores.
He must have drunk a tremendous amount.
Awakened by the train attendant, he opened his eyes.

He was still unsteady at the waist.
When he went to check the washroom, it was packed.
Outside the window, morning mountains and fields shone dazzlingly.

When he returned to the compartment, the berth had already been neatly put away. He had no appetite. Something was wrong. Why had he drunk so much like that yesterday? He remembered becoming severely intoxicated after sticking his face into the oden shop in Gunkan Yokocho. After that, it seemed a group had formed around him, and he kept drinking with someone—drinking on and on. With such a critical task at hand, his own behavior struck him as utterly inexplicable. It wasn't drunkenness—it felt more like anesthesia—Homura's body burned with remorse.

At Toyama Station, a large number of people got off.

Homura heaved his unsteady body up and disembarked.
He stepped outside but still felt unwell.

He finally mustered his resolve and rushed into the station-front police box.
It was deeply mortifying, but he’d reasoned that if he pushed himself too hard and committed an even greater blunder, he’d never be able to face the client of the case.

When he showed his identification, the duty officer at the police box called headquarters for him.
Soon, a detective named Kuriyama and another doctor arrived to collect Homura.

“This is the effect of a paralytic drug.”
“Someone slipped you a dose, I see.”
“I’ll administer an injection right away.”

The doctor assumed a knowing look and began preparing the injection.

So it was true after all. That Yamashita fellow had been a fraud all along.

The image of Yamashita and his drinking companions lingering behind his eyelids—they were truly formidable men.
That his life had suffered no complications was his greatest relief.
Homura was laid down in the back room of the police box.

Detective Kuriyama went to the public hall on Homura’s behalf.
And what he had copied and brought back for him was the division problem shown above.

[Figure 8]

⑥

8□3

＿＿＿＿＿＿＿

74□)□□□□□□

□□□2

—————

□9□□

□74□

—————

□□4□

□□□□

――――

0

(End)

Moreover, seeing that the character 'End' had been written in a single stroke, it became clear that the treasure hunt of division problems had concluded here in Toyama.

When he looked at the division problem, the answer had finally reached the last digit.
The number 3 was there.
And it had been completely divided.
With this, the division was now complete.

Homura pressed throbbing temples and stared intently at the notebook.
He had to rapidly come up with an answer here.
The six-digit dividend still only had its first number identified.

“Mr. Homura.”
“Please drink this.”

The doctor poured hot liquor into a glass and brought it to Homura’s bedside.
When Homura tried to decline, the doctor laughed and said,
“No, this is the finest local liquor. If you down this in one go, it’ll actually perk you up faster.”
Homura picked up that thoughtfully offered glass and set to work on the final decryption.

[Figure 9]

⑥

HA NU

↓ ↓

8X3

＿＿＿＿＿＿＿

749)6CDEFG

↑↑ 5992←ニ

I RO ―――――

K9LM

↑

Ho

N74P

↑↑

HeTo

―――――

Chi

↓

QR4S

TUVW

――――

Ri → 0

First, he organized this as shown in Figure 9.
What immediately caught his eye was that multiplying the 3 appearing in the ones place of the quotient by the divisor 749 yielded 2247.
In other words, TUVW was 2247.
Seeing that it divided cleanly, V had to be 4 - and this point aligned perfectly.

Therefore QR4S also became 2247.
Furthermore G was equal to S at seven.

Now, what would be determined next?

"This doesn't make sense."

Homura's face contorted.

[Figure 10]

8X3

＿＿＿＿＿＿＿

749)6CDEF7

5992

―――――

K9LM

N74P

―――――

2247

2247

――――

0

He had progressed this far (Figure 10)—but the rest just wouldn't fall into place.
Homura groaned in pain and turned over.

"Why can't I solve this?"
"Have I gone stupid?"

Homura clenched his fist and struck his own head hard.

"No good. Can't solve it."

Homura thought he'd fallen into arithmetic hell.
If not that, then his brain must have gone completely numb.
Having unraveled this much - how could the solution still escape him?
Having dragged himself all the way to Toyama only to end up moaning in some police box backroom, he felt like the world's most wretched creature.
To hell with it all!

Gradually, the alcohol began to course through his body.
Whether from exhaustion or the alcohol’s effect, he began to doze off fitfully.

The riddle was solved.

When his eyes snapped open, he suddenly realized he felt remarkably refreshed.

He picked up the notebook again.

After staring intently at the notebook's cover for some time, he involuntarily—

“Hmm.”

He groaned and widened his eyes.

He rapped sharply on the tatami.

Detective Kuriyama, who had been waiting in the next room, burst into the room.

“Mr. Homura, what’s wrong?”

“Oh, Mr. Kuriyama. Can I still make the passenger plane to Tokyo departing today?”

“Huh? The passenger plane? Let me see—that departs at 1:40 PM, so forty minutes from now. What are you going to do about that?”

“I must return to Tokyo immediately.”

“Are you sure you’re in any shape for that?”

“No—I’m fine. The mystery seems close to being solved. I must return immediately. Please take me to the airport.”

The kind Detective Kuriyama supported Homura's body as he helped him into the passenger plane.

At 1:40 PM, the Universal aircraft departed for Tokyo.

Homura stuck his pale face out the window and waved to Detective Kuriyama, who was seeing him off.
And he let out a sigh of relief.

He had finally been deceived through four full days.

Homura's mind was unsettled.

What had become of the division key?

The key could be said to remain unsolved—and yet also solved.
For the anticipated six-digit number ultimately remained unknown.
It had been crafted to remain unsolvable.
Because two answers emerged.

The problem lay in the X occupying the second digit of the answer.
This had been narrowed down to either 5 or 9, but now he realized that 5 would suffice if acceptable, and 9 posed no problem either.
So there were two answers.

If X was 5, the required six-digit dividend became 638897.
If X was 9, it became 668857.
How could there be two valid answers for the code key?
There absolutely had to be only one.
It was there that Homura understood everything.

"Damn—they tricked me completely."

He felt as though waking from a dream for the first time.
Why had they deceived him?
What had his enemies intended to do with him?
Everything remained a mystery.
He realized solving it required returning to Tokyo immediately—there was no alternative.

It seemed that Tokyo was lying in wait with a major incident beyond even his imagination.
What on earth could it be?

Homura arrived at Haneda Airport at 4:00 PM.
He immediately picked up the telephone and called Administrative Officer Kimura.

However, to his surprise, the Ministry of Home Affairs responded that there was no such person as Administrative Officer Kimura.
No matter how many times they went back and forth, the conclusion remained unchanged—no such person existed.

Even Homura paled.
Until this very moment, he had believed Kimura to be an official in charge of the Ministry of Home Affairs' intelligence division—yet now, this man had vanished like a dream.

Realizing what was happening, he next called his own office.
Yet the call simply wouldn’t connect.
What could Ōtsuji, who should be keeping watch, be doing?
The unease grew increasingly intense.

Having concluded this was the end, Homura exited the airport, hailed a vintage taxi, and had it rush full speed toward Tokyo.

Administrative Officer Kimura had vanished, the office was empty, and Ōtsuji was gone.
And I had been dragged all over for four full days by these bizarre numerical riddles.
What in the world was this?

"Ah, I see."
They'd taken advantage of my carelessness and skillfully deceived me.
Right—I was starting to piece things together now.
"They're those bastards from that secret organization!"

Homura's face gradually reddened.

Upon returning home, Homura immediately contacted various parties and gathered information.
And regrettably, he could no longer deny that he had been deceived.

Everything became clear through the explanation of an expert who had immediately rushed over.
The ones who had deceived Homura were indeed the spies from that secret organization.
It became clear that both Kimura and Yamashita were members of that organization.

The final remaining mystery was why they had dragged Homura around for four full days like this.

“You already know that, don’t you? It’s the shortwave radio in your office,” the expert declared, pointing squarely at the star.

“Wh—what—”

“Well, with that communication device confiscated, they lost their wireless link between Tokyo and Shanghai. That’s when they set their sights on your shortwave radio. That’s why they kept you away from your office for four days. During that time, those bastards undoubtedly used your machine to conduct critical communications. Now that you mention it, there’s something that comes to mind on our end.”

Even Homura gasped in shock upon hearing this.
So those spies had their sights set on his shortwave radio?
"Then what happened to Ōtsuji, who was keeping watch?"
A week later, Ōtsuji returned to Homura as a cold corpse.

How had it come to this?

The circumstances during that period were later revealed through Ōtsuji’s journal, which Homura discovered among the account books. On it, in hurried pencil, was written as follows.

"Due to a message stating Master had been gravely injured and required my immediate presence, I am departing.
August 26, 11:37 PM"

With this, all became clear.
The spy organization must have lured Ōtsuji away by claiming Homura had suffered severe injuries - since they couldn't use the shortwave radio while he remained at the office - then eliminated him.
As for Ōtsuji himself, being no man to submit quietly to confinement, this was likely what brought about his tragic end.

“And so, I was completely manipulated—suffering humiliation, committing grave blunders left and right—even now, just recalling it makes cold sweat break out from under my arms.”

Having finished recounting the unprecedented code numbers case, Homura let out a deep sigh.