Pathway to Japanese Literature

1

For Houmura Souroku, the up-and-coming young detective, this remained the great disgrace of his life—something he couldn't dismiss no matter how desperately he tried. Even one of Detective Houmura's stature had allowed the murderer to escape—this killer who had sat within arm's reach for hours, close enough to apprehend with a mere stand and stretch. No—worse yet—Detective Houmura had utterly failed to notice the murder unfolding directly before his eyes from first act to final curtain, making his bitter resentment entirely justified.

"This is exactly why getting obsessed with every little competition is no good…"

From how he still clicked his tongue in frustration whenever he relived it, the memory appeared to be something truly unforgettable.
The details of that scene—which he had absentmindedly watched without recognizing it as a murder case—were approximately as described next.

＊ ＊ ＊

It was a muggy midsummer night.

The vigorous new district of Shinjuku—as if it had drawn in all the vitality of greater Tokyo—simmered as though in a vat of boiling oil.
Amidst that heat, young people living in suburban residential areas like A Town, B Town, and C Town stretching beyond Shinjuku walked along the pavement, pushing and jostling each other.
Suburban homes also appeared surprisingly lacking in coolness.

Detective Houmura cut across the pavement, entered a narrow path between large buildings, and pushed open the door of a house at the dead end adorned with a beautiful electric sign that read "Mahjong."
He was in remarkably high spirits, undeterred by the sweltering heat.
This was because the previous night, with the weight lifted from his shoulders after finally resolving a certain major case that had long troubled him, and with the joy of savoring his first day off in ages, he was frolicking like a child.
For three years now, he had been hooked on mahjong, and tonight he intended to battle it out to his heart’s content.

“Oh no, this is bad!”

Houmura shouted as he threw open the curtain to the mahjong club’s game room.
In this heat, it was literally packed to capacity with not even room for a pin.

“Welcome! It’s Saturday night, see? That’s why it’s packed like this, Professor!”

Toyo-chan the mahjong girl wiped the bead-like sweat that had broken out on the tip of her nose with a crumpled handkerchief as she spoke.

“I’d like you to stop with the ‘Professor—’ thing, Toyo-chan. Even though Mr. Hoshio Shinichirou is an actual professor, you go around calling that guy ‘Shin-chan,’ ‘Shin-chaaan’…”

“That’s not fair, Professor!” Toyo-chan protested, her ears turning crimson as she tried to shut him down. “Mr. Hoshio is here right now. If he heard that, I’d be in a real fix!”

“There’s nothing to worry about, Toyo-ppe-san,” Houmura chattered even more cheerfully. “If this gets heard, your goal will be achieved faster. Or should I really go tell Shin-chan? ‘Toyo-chan here is actually stirring up some old-fashioned trouble—what would the Professor say about that?’ But if you don’t swear not to call me ‘Prof,’ then I won’t help you.”

“There’s no such thing!”

“Toyo-chan, recooord!” Houmura called out.

“Coming right away!” she answered, then turned to Houmura and said in a low voice: “That Shin-chan’s group has been playing in the special room since noon again today. Won’t you join them over there, Mr. Houmura?”

The "special room" was a long, narrow annex adjacent to the main hall. Four mahjong tables stood spaced comfortably apart, their chairs and tiles selected from rather high-quality materials—a touch of luxury accentuated by white silk tablecloths.
When Houmura entered, every table was occupied.
At the window-side table, the four members of Toyo-chan’s so-called "usual group" sat gathered around a single surface, absorbed in their game.
Houmura leaned against a nearby bench, forced to wait until a seat became available.
He found himself unconsciously facing toward the direction of the "usual group," though not truly observing them.

“This stifling heat must be because of the sunspots,” said Associate Professor Hoshio Shinichirou of the science university, who sat with his back to the entrance curtain near the front, clattering the mahjong tiles as he shuffled them.

“I say we kick those damn sunspots out of the sky! —Hey, look what I pulled!” The cheerful voice belonged to Matsuyama Torao—one of the group members, a Keio boy and swimmer seated across from Associate Professor Hoshio.

"I haven't gotten a single good tile all day," sighed Kawaoka Midori from Matsuyama's left side, her lips—which looked drenched in crimson—pursed tightly in frustration. And she extended an upper arm as pure white and glossy as ivory, discarding a tile.

“Ron!” cried Sonobe Hisakazu—the beautiful youth nicknamed Bean-chan—as he revealed his hand. Though called a youth, he was a second-year architecture student at university, making him the youngest among the male companions. Yet Kawaoka Midori, being nineteen, was actually his senior in age.

“Mr. Sonobe, open the window—it’s so hot.” Midori—nicknamed Miss Fox—raised eyes framed by slightly upturned, swollen eyelids as if in pain to make her request. Sonobe, who had been sitting in the farthest corner, stood and clattered the window open. A strong wind swept through the room.

Just then, one of the tables became available, so Houmura joined the group and began playing.
Since his seat directly faced the usual group's table, he would occasionally look up from gripping his tiles to peer at Associate Professor Hoshio's hand from behind or steal glances at Kawaoka Midori's snow-white nape, finding himself not entirely displeased.
Then as Houmura gradually became absorbed in the game itself, he found himself unable to observe every action of the usual group members from start to finish—though upon later reflection, certain subsequent details proved impossible to disregard.

The first was that mahjong girl Toyo-chan had entered and leaned against Associate Professor Hoshio’s back, maintaining a forward attitude for an extended period—Houmura found it amusing how Hoshio in turn adopted a visibly irritated demeanor.

The second was Matsuyama’s sports-driven habit of shouting

“Damn it!”

and yanking mahjong tiles from the table pile toward himself. Upon close observation, each time he would vigorously rub his thumb across the tile engravings. One might have wondered whether the pad of his thumb wasn’t growing sore from this. It was his particular vice.

The third was when Associate Professor Hoshio, leaping up in joy over a major win, accidentally knocked over Sonobe’s teacup next to him. A commotion broke out—moving the mahjong tiles aside, wiping the wet spots, having someone bring a new tablecloth, the four of them pulling at its corners and securing it to the table with rivets—it was a noisy affair. At one point,

“Agh! That hurts!”

When Matsuyama shouted loudly, they looked and saw him licking the tip of his finger. It seemed he had done something rough. It seemed someone had jeered at this, and a roar of laughter erupted, but for some reason, the group fell into deep silence afterward.

“What’s wrong, Ms. Midori? What’s troubling you?”

When Sonobe called out to Midori across the table in that shrill voice, Houmura jolted reflexively.
Looking up—what was happening?—Kawaoka Midori’s face had turned ghostly pale.
The skin that normally glowed with translucent whiteness now appeared utterly bloodless, as if one were gazing through layers of frosted glass.
Sonobe, his own complexion equally pallid, furrowed his brows in concern as he stared into Midori’s face.

“You should have a doctor examine you quickly—I’ll go call one right now...” Sonobe said, looking so worried he couldn’t sit still.

“Ms. Midori, are you feeling unwell?”

Associate Professor Hoshio paused his game and spoke.

“It’s fiiine—I’ll be better in no time.”

“But… you really should have that checked, right, right?” Sonobe urged, poised as if about to dash off at any moment.
Houmura had a realization.
While it was public knowledge that within their group, sportsman Matsuyama Torao and Associate Professor Hoshio were rivals for Kawaoka Midori’s affections, Houmura had once caught wind of rumors that Sonobe was actually in love with her too—and this now appeared to be true.

“I-I-I...” groaned Matsuyama, who had been sitting silently until that moment, his voice tight with pain. “I have a headache. I feel dizzy. I want to rest... Ugh...” Having said that, he stood up and staggered out of the room. “How peculiar—this place has turned into a sickroom,” Hoshio muttered with a hollow laugh.

Matsuyama’s vacant seat—like a missing tooth—evoked an unpleasant sensation in Houmura’s gaze.
It formed an ominous tableau.
Having deliberately shed his detective mentality to play mahjong—expecting carefree ease—he found himself unable to deny that his mind had somehow become disordered without notice.
From a mahjong table where four players should have been seated—wasn’t it perfectly ordinary for one to rise and visit the restroom?
Then why did this triviality nag at him?
Yet when retracing events since arriving at this club—hadn’t he intended immersion in gameplay while actually fixating on neighboring tables throughout?
He remembered how Kawaoka Midori had vacated her seat upon first entering this room—presumably visiting the facilities.
But at that time no suspicion had stirred.
Why did it unsettle him now?
The vacancy remained singular—but perhaps Midori’s current pallid discomfort transformed its significance?
If so—might he too harbor genuine affection for Midori? Like Sonobe...Hoshio...Matsuyama...

Speaking of Matsuyama—why hadn’t he returned? Why had Matsuyama suddenly fallen ill with headaches and such after Kawaoka Midori turned deathly pale? Was Matsuyama truly sick? Houmura became aware that various doubts had welled up within his mind without him noticing. No—this was merely an overzealous detective’s professional instinct. Hadn’t tonight been meant for forgetting work and simply playing mahjong? He wouldn’t dwell on trivial matters.—

Before long, the three who had been left behind—Hoshio, Sonobe, and Midori—perhaps having given up on vying for victory, left the table and exited the room. Detective Houmura, finally able to adopt a carefree mindset, became engrossed in the game.

2

The match at Detective Houmura’s mahjong table also ended about thirty minutes later.

In the final round, he made a foolishly lucky win, earning about three thousand points total over two games and feeling somewhat pleased with himself.
When he left the mahjong table and looked around, all other tables had already been vacated by departing guests, their variously colored tiles messily scattered across the white square cloths.
Checking his watch revealed it was slightly past eleven.

In the adjacent hall too, the customers had already thinned out.
Toyo-chan, her face sleepy, was keeping the clerk from a nearby store company.

“Goodbye, Toyo-chan.”

“Goodbye, Mr. Sensei—no, Ho-san!”

“Have they all gone home already?” Houmura found himself asking what didn’t need to be asked.

“Ms. Midori, Mr. Sonobe, and Shin-chan—they just left saying they’re heading home now.”
“Only Mr. Matsuyama should be sleeping in the back.”

“What? So Mr. Matsuyama was actually ill?”

Houmura made a face that said he found this unexpected.

“Oh? Why do you ask?”
“He says he’s feeling just awful.”
“I asked earlier if we should call a doctor, but he said it wasn’t necessary.”
“Shin-chan and the others stayed to look after him for a while, but when it got late, they said they’d leave things to us and went home.”

“That’s rather heartless.”

“But Shin-chan and the others live far away. Only Mr. Matsuyama lives right nearby, so it’s fine to leave him be, you know.”

Toyo-pe attempted a sympathetic defense of Shin-chan and the others’ suburban lifestyle.

“Well then, maybe I’ll go check on him.”

Detective Houmura opened the small door beside him and clattered down the narrow staircase.
At the bottom of the stairs was a narrow hallway, with a vast room lying beyond.
This served as the shared bedroom for everyone in the building.
When he slid open the shoji screen, there indeed lay a single futon spread out.
Despite his claimed headache, Matsuyama slept with the bedding pulled completely over his head.

“Mr. Matsuyama, Mr. Matsuyama—how are you feeling?”

Houmura gradually raised his voice louder, but Matsuyama gave no response whatsoever.

(He’s sleeping soundly…)

Houmura quietly closed the shoji screen and took two or three steps back toward the staircase.
But then—for reasons unknown—he suddenly turned back, swung open the shoji screen with a clatter, and stomped in his shoes toward Matsuyama's futon. Taking a lighter from his pocket, he clicked it alight, quietly held the flame toward the pillow area with his left hand, while stretching his right hand to firmly grab the bedding's collar and gently lift it.

“Gah—”

The face illuminated by the lighter’s pale yellow glow was undoubtedly that of Matsuyama Torao, yet no trace remained of that vibrant, cheerful sportsman Matsuyama. The visage had swollen into a livid purplish-black hue, both eyes snapped wide open in a fierce stare fixed upon some unfathomable distance. Within the gaping mouth frozen mid-gasp hung a tongue bereft of elasticity, dangling limply. Against rows of pure white teeth clung a sticky brown liquid, half-dried like congealed resin.

He’s completely dead—it seems to be death by poisoning.
Suicide or murder?…

True to form, he showed no panic, raised no loud voice, but with a deep furrow between his brows, he seemed to be organizing his thoughts about something for about five minutes.
From where did the wind come? As the small flame of the lighter flickered unsteadily, inky black shadows of varying hues formed upon the corpse’s face. A visage so ferocious it resembled a demon—an entirely different person—took shape layer by layer, appearing to rise from the tatami mats and assail Detective Houmura.

Before long, the detective quietly stood up, exited the room where Matsuyama lay dead, and clattered back upstairs.
He was neither "Sensei" nor "Ho-san" anymore.
That was completely restored as Houmura Souroku, the renowned detective who held the key to the dark underworld of the imperial capital.

He quietly called for Funaki Toyono—not Toyo-chan the mahjong girl—and briefly informed her of the tragedy downstairs.
Although he had told her not to make a sound,

“Oh my! Mr. Matsuyama is dead!”

Shocked by this exclamation, those who remained quickly grasped that an incident had occurred and tried to rise from their seats en masse. Detective Houmura had no choice but to announce his authority. “My apologies for the inconvenience,” he declared, “but I must request that everyone remain in this room without taking a single step outside until the officials arrive and complete their initial investigation.” With this pronouncement, he restrained the group.

Meanwhile, he urgently reported this unnatural death to the jurisdictional police by telephone and had the building custodian—who had been waiting in another room—temporarily guard the chamber containing the corpse. Then he urged Toyono, whose face threatened tears at any moment, to stand watch at the special mahjong room’s entrance while keeping everything inside precisely as it was.

“Do you know where Shin-chan and the others live?”

Houmura asked Toyono.

Toyono appeared hesitant for a moment, then gave a silent nod.

Houmura thought it necessary to summon the three persons of interest—Hoshio, Sonobe, and Kawaoka Midori, who had left earlier—to this location as soon as possible.
According to Toyono’s account, the three would take a city tram from here along a road stretching about fifteen chō to the terminus, transfer to an express train there, and at the third stop—Station A—Hoshio would disembark. His boarding house was said to lie in the shadow of a broad hill, reached after walking about five chō along a dim country road.
Sonobe would get off at the next station, B Station.
His house stood right by the station, where he lived with his parents.
At the next station after that, C Station, Kawaoka Midori disembarked.
About three chō diagonally from the station entrance lay her aunt’s house, where she was said to be staying.

Detective Houmura made another call to the police station, expressing his hope that they would intercept their return home and bring them back to the scene immediately—a request that was promptly approved.

3

Detective Houmura Souroku, as if begrudging every second, went downstairs and meticulously examined Matsuyama's corpse.
There was nothing particularly noteworthy except one discovery—a shallow wound on the pad of the right thumb, as if pricked by a needle, with only its surrounding area swollen in a wart-like manner and showing slight redness.
This was likely the wound Matsuyama had cried "Ouch!" about when replacing the white cloth cover, though when exactly this injury had formed remained unclear.
Whether the poison had entered through the mouth, been injected, or infiltrated through such a wound posed an intriguing question—one that led Detective Houmura to regard this injury with particular significance.

When he had finished examining the corpse, he returned upstairs and conducted a thorough investigation of the mahjong table used by Matsuyama and the others. He paid particular attention to the area where Matsuyama had been sitting, pulling at the cloth, removing rivets, and using a brush to gather dust into several paper packets. Then he crawled under the table, pressing his face almost against the floor as he examined various spots. He cut blotting paper into four pieces, pressed them firmly onto areas of the floor that seemed to have been under the four people’s feet—appearing to absorb something—then made these into separate paper packets marked with pencil symbols. As he tried to crawl out from under the table, he suddenly noticed the head of a rivet—its pin missing—lying in the shadow of the table leg that marked the boundary between Midori and Matsuyama. He carefully picked it up with tweezers.

Once that was done, Detective Houmura picked up each tile one by one and examined them in detail.

Just then, as the prosecutor and members of the investigation division arrived, he temporarily halted his examination of the tiles and guided the group to the room containing the corpse.
Immediately, through an examination conducted by the police doctor, it became clear that the cause of death was poisoning.
The fact that less than one hour had passed since death was proven by the lukewarm body temperature remaining in the corpse's armpits and Houmura's testimony.
However, what poison had been used and where it had entered could only be determined through an autopsy.
Houmura drew the officials' attention to the wound on the pad of the thumb.

An investigation was conducted around the mahjong table as well, but it was not as thorough as the one Detective Houmura had conducted.

And so began the official inquiry into Matsuyama Torao’s suspicious death incident.
Detective Houmura explained to Prosecutor Karigane and Chief Investigator Kawaguchi what he had witnessed that night regarding Matsuyama and the others’ movements.
This was exactly as described at the beginning of this story, but he did not fail to add that Detective Houmura had likely overlooked a considerable number of facts.

Among the various opinions expressed, all agreed on one point: Matsuyama had not committed suicide.
He was not predisposed to such acts; no suicide note had been found in his pockets; his bankbook contained substantial deposits; moreover, there were two letters—one from Midori's younger brothers stating they would go to the Jingu Gaien entrance at 10:30 tomorrow as their "big brother" had instructed to watch the swimming meet, and another from Midori's father containing a letter of gratitude reading "I am deeply obliged for your continued support of the children's educational expenses," accompanied by a provisional receipt for fifty yen.
That someone in such prime condition would take his own life was inconceivable.
Furthermore, this conclusion was expected to be definitively confirmed through examination of his desk and an autopsy of his body.

If we tentatively concluded that Matsuyama Torao had been murdered by another person, then considering the circumstances before and after, the first suspects would naturally be his three mahjong companions—the question being who among them had administered the poison to him. However, regarding those three individuals, the officials had not obtained what could be considered conclusive evidence.

Prosecutor Karigane said:

"What's odd is that Kawaoka Midori became unwell around the same time as Matsuyama's death. Furthermore, according to letters found in Matsuyama's pocket, it appears he held considerable authority over Kawaoka Midori—yet these two facts seem to contradict each other..."

“I’m also unclear about the relationship between those two,” said Chief Investigator Kawaguchi.
“Let’s just ask the mahjong parlor girl.”

Toyono was summoned and ordered to disclose everything she knew about the aforementioned companions.
It was generally not much different from what Houmura had previously stated, but she added the following.

“Mr. Matsuyama provides substantial financial support to Ms. Midori’s household, I hear.”
“It seems there have been discussions between Mr. Matsuyama and Ms. Midori’s father about her marrying into his family.”
“However, it appears Ms. Midori doesn’t care much for Mr. Matsuyama.”

“Then who does Ms. Midori like?”

Chief Inspector Kawaguchi inquired.

“Well, that’s…” She hesitated, clearly flustered, then answered, “Who could it be? I really don’t know.”

Detective Houmura seemed to have an idea about the circumstances behind Toyono’s hesitation.
She probably knew that Midori, like Toyono, had some affection for Associate Professor Hoshio.

The prosecutor interjected, “Who did you hear that from?”

“Mr. Sonobe was the one who said that.”
“Since Mr. Sonobe lives nearby, he must know well, wouldn’t he?”

After dismissing Toyono temporarily, Prosecutor Karigane said.

“This seems to explain the contradictory facts we had earlier. Midori is bound by money and her parents and has to marry a man she dislikes.”

“Then, if Midori poisoned Matsuyama,” Chief Inspector Kawaguchi countered, “by what method did she do it?”

“If Matsuyama let his guard down, it would be a simple matter for Midori to put poison in his teacup.” “You—I’d like you to have the teacup Matsuyama used analyzed.”

“If I may interject,” said Detective Houmura, who had been silently arranging the face-up mahjong tiles on the table by type and scrutinizing their surfaces. “By arranging the tiles in such an orderly manner, I’ve made a discovery. Look here—there are four nine bamboo tiles lined up in this spot. Now, one of these four has paint on its carvings that’s faded noticeably compared to the other three. Generally, when water gets on tiles, it causes some color to peel off—but examine this closely. Not only has it peeled; what was originally red has turned black, and blue areas have taken on a yellowish tint. This wasn’t caused by water peeling. We must imagine someone applied a foreign substance—another chemical agent.”

“Well, well—this is an interesting discovery.”
“So the culprit applied poison into the carvings of the mahjong tile, then,” Prosecutor Karigane exclaimed.

“However, how did that enter Matsuyama’s body?”

“There was a small wound on the pad of the corpse’s thumb,” Chief Inspector Kawaguchi interjected. “Do you think poison in deep engravings could easily enter the body through such a wound?” he asked Houmura.

“The culprit’s preparations were quite ingenious,” said Detective Houmura, biting his lower lip as if recalling something. “Matsuyama Torao had a habit of pressing down hard and rubbing the carved areas of tiles with the pad of his thumb when drawing them. Tonight too, because he rubbed the poisoned tile with great force, we believe the poison entered through that wound.”

“This makes perfect sense,” Prosecutor Karigane declared, striking his gavel.

“Based on my experience,” Detective Houmura said through pursed lips that betrayed suppressed excitement over his deduction’s elegance, “this poison was extracted from African Strophanthus grass.” His index finger tapped rhythmically against his notebook’s edge—a metronome underscoring forensic certainty. “The natives apply it to spear and arrowheads when fighting enemies.” A pause stretched taut before he delivered the clinching detail: “When introduced through wounds? Cardiac arrest.” His voice dropped conspiratorially on adding: “Requires mere micrograms for lethality.”

“How on earth did Kawaoka Midori obtain such poison so easily?” said the chief inspector skeptically.

“I have not yet concluded that Midori is the culprit,” protested the prosecutor.

“And there’s something even more interesting,” Detective Houmura continued undeterred. “When I examined the tiles through a magnifying lens, I made a crucial discovery. At the carved edges, there are two or three thin white fibrous lines adhering to the surface. This indicates what material the culprit used to wipe away the poison afterward. After performing a basic test on the substance I collected with tweezers, I confirmed it was cotton wool.”

Detective Houmura’s theory was so lucid that the prosecutor and chief inspector fell silent, bereft of any words of admiration.

“However,” Detective Houmura said, suddenly appearing dejected as he changed his tone, “my theory merely explains the method by which the culprit killed Matsuyama.”
“Who killed Matsuyama has not been determined at all.”
“Despite leaving behind so much evidence, there isn’t a single clue at present that identifies the culprit themselves.”
“The culprit must possess an extraordinary genius when it comes to crime.”

Even so, the method of the crime that Houmura had solved in such a short time was undoubtedly going to prove extremely useful for future interrogations.
In that regard, the prosecutors commended Houmura.
Just then, the detectives who had gone to search for the three came clamoring back.

4

The subsequent interrogations were commenced at the same location from the afternoon of the following day.

“The autopsy on Matsuyama’s body has determined it was murder, not suicide. The poison entered through the thumb, just as Mr. Houmura theorized—the cause of death was cardiac arrest, and the poison appears to be Strophanthus. All of which aligns perfectly with Mr. Houmura’s theory.”

Chief Inspector Kawaguchi was the first to report.

“Then I shall give my report as well,” said Detective Houmura in an uncharacteristically subdued tone.
“Having examined various materials collected near the mahjong table, I found no leads whatsoever regarding the culprit.”
“This is most regrettable.”
“The sole item I wish to present is this rivet head”—here he indicated the rivet head missing its pin, which he had retrieved near the table leg the previous night—“which bears relation to the crime.”
“Observe—this rivet head has been filed down remarkably thin.”
“This was done intentionally. With a small hole drilled into its surface, pressing this rivet forcefully into the mahjong table using one’s thumb pad would cause the needle—its supporting metal now too flimsy—to reverse direction and stab clean through the thumb.”
“Thus did Matsuyama unwittingly create precisely the wound upon his thumb that the culprit required.”

“That’s commendable work,” said Prosecutor Karigane.
“Did any of the culprit’s fingerprints remain?”

“Matsuyama’s fingerprints are clearly present, but no one else’s could be found.”

“So the culprit was lying in wait for an opportunity to make Matsuyama use that rivet,” said Chief Inspector Kawaguchi.

“To make them use that rivet, the culprit had them overturn a teacup and replace the white cloth.”

“Hmm, that’s—” The prosecutor flipped through his notebook’s pages. “Hoshio Shinichirou was the one who overturned the teacup. Suspicion falls on Hoshio.”

“But Prosecutor Karigane,” Houmura said, “the teacup could have been positioned where it would be overturned.”

“So if it was Sonobe’s teacup, that makes Sonobe the culprit,” Chief Inspector Kawaguchi laughed mockingly.
“Isn’t that rather overcomplicating things?”
“Rather than that—since the culprit must have been constantly carrying poison, rigged rivets, and the cotton wool that Mr. Houmura’s theory identified as being used—all to seize the opportunity for murder—I think we should inspect the belongings of the three people detained last night.”
“Actually—in fact this morning—a report came in from one of my subordinates—the cotton wool in question has been found.”
“We even know who had it.”

The prosecutor and Detective Houmura were stunned.

“That would be Hoshio.”
“Actually, when the detective sent to apprehend Hoshio was escorting him here, he stealthily pulled something from his pocket and tossed it by the roadside—my subordinate quickly retrieved it.”
“It bore a tea-brown stain.”
“The forensics team confirmed it carried traces of the poison in question.”

“Have you pressed Hoshio yet?” asked Prosecutor Karigane.

“We confronted him immediately.
But he refuses to confess.”

“Well, of course. Hoshio’s motive for killing Matsuyama is slightly too weak.”

“Not necessarily, Mr. Karigane. Hoshio is a science professor. He should be well-versed in scientific matters. Moreover, Hoshio’s father resides in Kobe, where he runs a spice and perfume wholesaler that procures various raw materials for perfumes from tropical regions and sells them. They have ample means to procure pharmaceuticals from Africa. Additionally, Hoshio is rumored to have somewhat deviant sexual tendencies. And after all, it was he who overturned the teacup. The reason his crime scene didn’t enter Mr. Houmura’s sight was because Mr. Houmura was facing away from it.”

Indeed, Houmura—being positioned where he could clearly see Hoshio’s tiles—had fixated solely on that aspect and paid little attention to his actions.
The evidence the Chief Inspector had presented was indeed sufficient to cast strong suspicion upon Hoshio.

At that point, Hoshio was dragged out before everyone. They pressed him to confess about the source of the cotton wool and poison, but he stubbornly refused to speak as they wished. However, as the chief inspector pressed relentlessly on his vulnerable spots in a practiced manner, even he could no longer endure it—it seemed—and finally began to speak. That was the kind of matter the prosecutors had never anticipated.

“Actually, I stole that cotton wool from Ms. Midori’s sleeve while we were playing mahjong.”
“I have no knowledge regarding the poison.”

As Hoshio turned red and pale while recounting his story, it couldn’t be dismissed as an outright lie.
He professed profound shame regarding his deviant sexual proclivities and wiped his sweat.

Though this didn’t fully clear him of suspicion, they resolved to question Midori about both the cotton wool and poison.
In a somewhat disheveled state, she was assisted to her seat by the detective who had escorted her there the previous night.
Under interrogation, she offered this account.

“I’ve been… since yesterday,” she faltered slightly before continuing, “actually menstruating.”
“So shouldn’t it be perfectly natural for me to have cotton wool?”
“I know nothing about any poison.”
“Are you suggesting I wanted Matsuyama dead? That wouldn’t be an unwelcome outcome for me.”
“No matter how fine a man he might be, I loathe being traded like merchandise through monetary arrangements.”
“However, I have absolutely no memory of killing Mr. Matsuyama.”

In the course of the investigation, they called Sonobe in for questioning.
From start to finish, he answered that he didn’t know.
When Midori had confessed to possessing the cotton wool and they asked him, "Do you know about this?" he vehemently denied it, saying, "That's a lie."
Upon questioning, it became clear he was a young man who even lacked knowledge about menstruation, prompting the chief inspector to burst into mocking laughter.
They asked if he knew that Hoshio had possessed the cotton wool, but he again said, "I don’t know."

Then the detective who was accompanying them interjected.

“This individual here noticed Hoshio discarding the cotton wool and alerted us,” said the detective. “To tell the truth, I went to apprehend him but ultimately couldn’t find him and returned empty-handed. However, Detective Honda—who had gone to search for Hoshio—discovered Hoshio and this person walking together along a dark country road and brought them back. During that process, he mentioned having noticed when Hoshio discarded something.”

The detective was summoned and affirmed that it must be so, intending to report later—but then he produced a nickel-plated paperweight measuring five or six inches in length, stating they had discovered such an item from Sonobe’s pocket. According to Sonobe’s defense, he had bought it from a night stall vendor who was about to close shop near B Station.

“Why didn’t you get off at B Station and instead got off at the previous station, A Station?” Houmura interjected from the side at this moment.

“That night, because I was feeling uneasy, I intended to take a short walk with Hoshio-kun,” Sonobe answered in crisp tones.

Next, as a precaution, Mahjong Girl Toyono was to undergo questioning.
As they continued questioning her about various matters, Toyono finally broke down in tears, but what she stated last threw the investigators’ minds into complete disarray.

“I saw Mr. Hoshio steal cotton wool from Ms. Midori’s sleeve,” she said. “I was so frustrated that I went around behind him and stole that cotton back. I rolled it up tightly and threw it in the wastebasket—if you search there, you should find it.”

The cotton wool was indeed found in the wastebasket.

This discovery meant suspicion regarding the cotton wool had now reverted back from Hoshio to Midori. If the cotton stolen from Midori had passed through Hoshio’s hands to Toyono’s, then where had Hoshio obtained the poison-tainted cotton he discarded on that country road? The only conclusion was that he must have possessed it from the beginning. That Sonobe hadn’t disposed of it was confirmed by Hoshio’s own confession of possessing the cotton wool—though Hoshio appeared unaware that Toyono had stolen it from him.

Now, the focus of the case converged on the origin of the cotton wool.
Apart from what Midori had prepared, there existed cotton wool that Hoshio had brought from somewhere with poison adhered to it.
However, the key to confirming its origin was nowhere to be found.
Therefore regarding Matsuyama’s killer—they considered Hoshio most plausible as primary suspect, Kawaoka Midori secondary, Sonobe tertiary—and though Toyono likely wasn’t culpable—they tentatively listed her fourth—yet no decisive evidence emerged to confirm any.
The case had literally entered a labyrinth.

5

That night, Detective Houmura holed up in his laboratory and repeatedly reviewed the case from its beginning through that day's investigation. When he thought about it, compared to the strong suspicions surrounding Hoshio and Midori, he had hardly considered Sonobe at all. However—was there truly nothing worth doubting? Detective Houmura temporarily shifted his suspicion to Sonobe and reconsidered the murder as a disguised act.

There was no definitive evidence, but if he entertained suspicion: (1) that Sonobe had intentionally placed the teacup where it could easily be knocked over; (2) that his extreme panic when Midori complained of feeling unwell stemmed from fearing the poison he'd applied to the tile might have affected her; (3) that his corner seat allowed easy secret application of poison and subsequent wiping with cotton wool; (4) that informing detectives about Hoshio dropping cotton—while remaining silent on other matters—couldn't be deemed entirely above suspicion; (5) that deliberately alighting at Hoshio's station while carrying a paperweight resembling a murder weapon was undeniably suspicious.

Yet these remained mere suspicions without physical evidence—so flimsy in foundation that any judgment day would see them dismissed as "insufficient evidence" by the court.

Repeatedly gazing at this numbered list, he suddenly—

“This is strange...”

he muttered.

(5) In the fifth item, he had pointed out that Sonobe had purchased a paperweight. But if this was something Sonobe had prepared intending to kill Hoshio on his way home, what sudden motive could have led him to resolve to kill him?
If he had used such an amateurish murder method, his actions should have been immediately exposed.
Though he was not someone who wouldn’t realize that, he had dared to do so—could it be that Hoshio had suddenly come into possession of something incriminating against him?
If the detectives hadn’t arrived in time, Hoshio might already have ceased to be among the living.

When he considered this, he wanted to meet Hoshio and question him.
After preparing, he immediately went to the detention cell and asked Hoshio if there was anything he had forgotten to state—particularly whether anything had occurred on the train.

Hoshio didn't seem to have anything particularly significant to add. He said what he'd forgotten to mention was merely that Sonobe had seen him hurriedly pick up the cotton wool he'd carelessly dropped on the train.

As a precaution, he had Kawaoka Midori brought out and asked if there was anything she had forgotten to mention; she answered with slightly more composure than before.

“I had forgotten a small detail,” she said. “When I was playing mahjong at the club, I happened to look under my foot and saw that cotton wool lying there. Thinking how embarrassing it was, I quietly picked it up. That happened just before we stopped. I definitely picked it up and should have put it in my sleeve, but when I checked later, it was gone.”

This clearly occurred after the first cotton wool had been stolen by Hoshio. That cotton wool had been tainted with the poison. This later came into Hoshio’s possession. There, Houmura conceived an idea and inquired.

“Where were you seated on the train?”

“Well, it was so unbearably hot and stuffy then that I opened the window in the passageway connecting to the next car to cool off. When the train picked up speed there, such a strong wind blew in that I finally started feeling better.”

Detective Houmura slapped his knee. At that moment, the cotton wool must have blown from Midori’s sleeve in the strong wind and rolled right to Hoshio’s feet. Since Hoshio didn’t know Toyono had stolen the first cotton wool, he likely mistook this for his own dropped item and hastily retrieved it. Now the issue had narrowed decisively—who had dropped the poison-laced cotton wool that Midori picked up at the mahjong club?

The reason Sonobe had developed an intent to kill Hoshio had now found its first coherent explanation.
That cotton wool was undoubtedly what Sonobe had used in the crime—he must have accidentally let it slip from between the folds of his hakama, where Kawaoka Midori then picked it up.
Yet even this—without his confession—lacked any concrete physical evidence.
Sonobe’s startling criminal ingenuity had succeeded in murdering one friend through an unorthodox method while managing to implicate two others under heavy suspicion.
Forcing a confession from Sonobe wouldn’t be easy.

Detective Houmura continued to let out pained groans as he pondered for a mere thirty minutes. Then, suddenly assuming a radiant expression, he rose to his feet. He summoned the night-duty officer, requested the attendance of Prosecutor Gankane and Chief Investigator Kawauchi, and had Sonobe brought forth.
Sonobe appeared before Houmura relatively energetically, his beautiful face grinning.
That utterly confident demeanor flared Detective Houmura’s antagonism.

With him before him, Houmura began meticulously recounting the details of the Matsuyama Torao murder case.

Even when his name was brought up, and even when the situation detailing his activities as a murderous fiend was described in detail, Sonobe did not change his expression in the slightest.

Detective Houmura was gradually growing uneasy about his own hypothesis, but he rallied his spirits with a "Just you wait" and played his final trump card.

“However, there was one thing the ingenious culprit failed to notice.”
“It’s this right here.”

With that, he picked up the head of a rivet—its needle detached—with his tweezers’ tip and declared:

“There were two fingerprints on this rivet head, you understand?”
“One is undoubtedly from the late Mr. Matsuyama Torao, who created the wound with this.”
“The other isn’t his.”
“It belongs to the culprit who orchestrated his use of this rivet.”
“This is the sole fatal evidence left behind by that meticulous criminal—the one who succeeded in destroying every other trace.”

“What do you say?”
“Does this ring any bells?”
“That’s right.”
“The culprit was so engrossed in wiping the poison applied to the tile with alcohol-laden cotton wool that he forgot to wipe away the fingerprints remaining on this rivet’s head.”
“Now then, Mr. Sonobe—I’d just like to take your fingerprints...”

Sonobe’s complexion abruptly turned deathly pale at this moment, and his body began to tremble violently—

“I’m sorry, Matsuyama!”

Having said that, he collapsed backward with a thud.

＊ ＊ ＊

“Didn’t you say there were no culprit’s fingerprints on that rivet’s head?”

Prosecutor Gankane later asked Houmura suspiciously.

“Well, that was—”

Houmura said while scratching his head.

“Well, that was strategic psychology.”
“Even a culprit who executed a crime with machine-like precision ultimately isn’t a machine—that’s the human flaw. When confronted with an unexpected accusation they hadn’t prepared for, their ‘anxiety’ swells like a towering cumulonimbus cloud until it reveals their true nature.”
“This is a method Chief Kawauchi often uses. I simply waited for the right moment to turn their own tactics against them.”
“But whether it’s reversing their methods or failing to see the crime unfolding before me—from start to finish, this has been my utter defeat.”