Chapter Sixty: The Wrong Tune

The mist drifted across the red brick wall of the funeral home, stretching Shen Mo's shadow into a thin, elongated line.

He gazed at the gradually sharpening figure in the grey cloth military uniform, his Adam's apple bobbing slightly as his phone vibrated hotly in his palm—an incoming call from Officer Zhou.

"Forensic Doctor Shen, pulling up architectural models in the middle of the night?" Officer Zhou's voice came through with the hissing sound of an e-cigarette being puffed on. "That stuff is locked up in the archives. I'll have to track down old Chen from the storage department..."

"Captain Zhou," Shen Mo interrupted him, pressing his knuckles against the frost on the windowsill. "You mentioned last time that the third night watchman died clutching his ears and screaming, 'There's a sound running through my bones.'" He looked down, flipping open the architectural blueprints, the tip of his pencil pointing at the U-shaped corridor behind the incinerator. "If the sound of a flute forms a standing wave in this kind of structure, the resonant frequency could be just enough to pierce the cranium."

The sound of an audible gasp came clearly over the phone.

Officer Zhou's police badge chain jingled against his collar, and Shen Mo could almost picture his furrowed brows—the officer who always burned mugwort at crime scenes was now massaging his temples while facing his computer. "Fine, I'll go to the precinct and pull the records now. But let's get one thing straight..."

"Thank you." Shen Mo hung up, and as he turned, the hem of his white lab coat brushed against the bone flute on the edge of the desk.

The scalpel made half a rotation between his fingers, precisely slicing through the seal of the laboratory's acoustic interferometer.

Three hours later, when Officer Zhou burst into the morgue holding a yellowed blueprint, Shen Mo was staring intently at the undulating waveforms jumping on the monitor. "The wall resonance frequency of the U-shaped corridor is 59.3 hertz." Without turning his head, he used a pair of tweezers to pick up the bone flute and point to the curved corridor on the blueprint. "It matches the time interval between the night watchmen's deaths perfectly."

Officer Zhou slammed the blueprint onto the table, the smell of printer ink mingling with the scent of tobacco on him. "The standing wave you mentioned... can it really make people hear a sound that doesn't exist?"

"Not hear it," Shen Mo pulled up a segment of audio. "The brainstem auditory center is being activated by resonance." He pressed play. First came a harsh buzzing sound from the speaker, which gradually peeled away to reveal a muffled male voice: "Wang Tiezhu, Li Guihua, Zhang Erniu..." The speech was as rapid as a machine gun. "Twelve people per minute, which matches the registration speed of the military doctor back then."

Officer Zhou's Adam's apple rolled. "What the hell is this..."

"It's Zhou Mingyuan's logging audio," Shen Mo turned off the instrument. "The bone flute is the medium, and the flute sound is the key. Every time it is played, it's equivalent to hitting the play button." He grabbed his coat and walked toward the door. "Now I need Old Wu's interrogation records."

When Old Wu was led into the interrogation room, his trouser cuffs were still stained with the damp mud of graves.

He stared at the ID badge on Shen Mo's chest, his fingers twisting the faded blue cloth shirt. "Offi... Officer, I was just helping to relocate the graves..."

"On the fifteenth of last month, you sold seven sets of remains for wine money." Shen Mo slammed the evidence bag onto the table. Inside was half a rib bone bearing saw marks. "Including Zhou Mingyuan's."

Old Wu's face turned instantly pale.

He opened his mouth, his Adam's apple moving three times before he could squeeze out a sound: "I—I only took seven... but that flute... there shouldn't be just one left!"

Shen Mo's pupils contracted sharply.

He pulled out his phone to check the cremation records, his fingertips sliding rapidly across the screen—the cremation dates of the unidentifiable bodies over the past three months: March 2nd, March 9th, March 16th... the interval was precisely seven days. "Logging the progress." When he raised his head, the hairs on the back of his neck stood on end. "We've already reached the seventh one."

The back alley of the funeral home gleamed coldly in the deep of night.

Xiaozhou crouched at the base of the wall, gently sifting fine sand between her fingertips.

Her canvas shoes were damp with dew, and her stray locks of hair brushed against the back of Shen Mo's hand as they fell—a silent signal meaning "ready."

Ah Huang lay flat in a corner, its ears perkily erect into triangles. Seeing Shen Mo nod, it lowered its head and snorted.

At 1:13 AM, the fluorescent hands of Shen Mo's wristwatch converged.

Fine ripples suddenly appeared on the sandy ground, and the first footprint clearly emerged: the tread of the military boot was deeply embedded in the sand, with the forefoot bearing more weight than the heel by two millimeters—matching the photograph completely.

Xiaozhou's sketchpad rustled softly.

At the seventh step, Ah Huang suddenly let out a low growl, its front paws fiercely scratching at the sand.

Shen Mo leaned in for a close look. Below the seventh footprint, there was an additional blurred semi-circle, as if someone had paused mid-stride while lifting their foot.

"Hesitation." He measured the stride length against the moonlight. "This should have been the handover point for the night watchman, but 'it' can't remember the exact location."

The vigil of the seventh night arrived faster than anticipated.

Shen Mo stood in the center of the corridor, the bone flute pressed against his lips.

He looked at the electronic clock on the wall, exhaling gently at 1:12:57—the third note should have been an F-sharp, but this time half a breath escaped, blowing it into an F-flat.

The sound-activated lights in the corridor flickered on and off in response.

The first six times had been a regular alternating rhythm of light and dark, but on the seventh time, the rhythm suddenly broke: the red light flashed twice before going out, and the yellow light was terribly slow to come on.

Shen Mo's eardrums ached fiercely, and a sound akin to fingernails scratching a chalkboard shrieked from within the walls—on the surveillance room monitor, the virtual footprints overlapped three times at the seventh step, like an old printer experiencing a paper jam.

"Registration error." As he lowered the bone flute, a thin layer of frost had condensed around its mouthpiece.

Under the microscope in the autopsy room, a few crystalline specks floated within his earwax—turpentine crystals, identical to the museum reverberation substance Su Wangying had mentioned.

"It's learning." Shen Mo's hand holding the glass slide trembled slightly. "We ended the previous obsession with negative space, so it learned to 'fill in the blanks.'"

The mist outside the window suddenly surged.

When Shen Mo looked up, he saw the leader of that row of figures slowly turning around.

The collar of the grey cloth military uniform was lifted by the wind, revealing a crescent-shaped scar at the collarbone—matching the curvature of the broken rib bone Old Wu had sold with absolute precision.

His phone vibrated on the desk.

Shen Mo swiped open the screen to find a message from Professor Lin: "We found Zhou Mingyuan's manuscript. Tucked inside the incomplete scroll is half a yellowed piece of paper..."

He didn't finish reading it.

Because within the mist, the young military doctor's hand was slowly reaching toward the registration ledger on his chest.

On the twelfth line of the blank page, the tip of a pencil was already pressing against the back of the paper, waiting only for the sound of a correct—or incorrect—flute.