The monitor went black.
Hae-in was already moving.
"Kang."
He turned.
She pointed toward the security camera above the hidden room.
"The indicator."
Kang looked back.
The tiny red light was gone.
"Someone shut it off."
"From where?"
He was already taking out his phone.
"I'll check the control room."
Hae-in stayed in the doorway.
She looked at the chair.
Nothing had changed.
The metal table.
The photographs.
The old camera.
The open door.
Everything exactly where they had left it.
Except for one thing.
The chair had moved.
Only a few centimeters.
Hae-in stepped back into the room.
Kang noticed.
"What?"
She pointed.
"I didn't touch it."
"Neither did I."
They looked at the floor.
Dust surrounded the chair legs.
One of the back legs had left a clean line through the dust.
It hadn't been moved recently by someone walking past.
It had been pulled.
From the table.
Toward the door.
Hae-in crouched.
There were marks on the floor.
Two parallel scratches.
Fresh.
She touched one with the tip of her glove.
"Someone was sitting here."
Kang looked toward the hallway.
"Recently?"
"The dust says yes."
He called the control room.
"Get me every camera covering Cell Block C for the last thirty minutes. Don't erase anything. Don't reboot the system."
A voice answered through the phone.
Kang listened.
His expression changed.
"What?"
Hae-in stood.
Kang lowered the phone.
"There's a problem."
"What kind?"
"The cameras didn't go offline."
He showed her the screen.
A security technician had sent him the system status.
Every camera in Cell Block C was functioning.
Except the one in the hidden room.
Hae-in stared at it.
"So someone accessed only that feed."
"Apparently."
"From the control room?"
"No."
"Then where?"
Kang looked at the technician's message.
"They're trying to find out."
Hae-in looked again at the photographs.
Seven people.
Seven names.
Seven lives reduced to evidence.
She picked up the photograph of Lee Ji-hoon.
There was something beneath it.
A small rectangular indentation in the dust.
She moved the photograph.
A brass key sat underneath.
No larger than her thumb.
There was a number engraved on it.
08.
Kang saw it.
"The Eighth."
Hae-in closed her fingers around the key.
"Maybe."
They returned upstairs.
The evidence room was locked.
Hae-in personally placed the seven photographs inside a sealed evidence envelope.
She logged the time.
12:47.
Kang watched.
"You're separating them?"
"For now."
"Why?"
"If someone gets access to one set, we don't lose everything."
He nodded.
She placed the key in another evidence bag.
ITEM 32-B.
Then she looked at the envelope she'd taken from the hidden room.
The Eighth.
Still unopened.
Kang noticed her staring.
"You want to open it."
"Yes."
"But?"
She looked at the evidence log.
"Someone left that envelope where we would find it."
"Exactly."
"So I don't want to read what they want me to read."
Kang pulled a chair out.
"Then don't."
She looked at him.
He sat down.
"We can figure out why they wanted us to find it first."
Hae-in sat opposite him.
She placed the envelope between them.
No dramatic warning.
No strange message.
Just paper.
Old.
Yellowed.
Sealed with clear tape.
Kang examined the edges.
"There's no return address."
"No name."
"Nothing on the back."
Hae-in held it beneath the desk lamp.
A faint impression appeared on the paper.
Not writing.
A shape.
A rectangle.
She turned the envelope over.
Again.
The same shape.
"There's something inside."
"Obviously."
"Something rigid."
Kang looked at her.
"You've been spending too much time with evidence bags."
She ignored him.
Instead, she photographed the envelope from every angle.
Then she opened it.
Inside was one sheet of paper.
And a photograph.
Hae-in removed the photograph first.
It showed the hidden room.
The same room they'd just entered.
The empty chair.
The table.
The seven photographs.
But the photograph had been taken from the doorway.
From inside the corridor.
Hae-in turned it over.
No date.
No message.
Only:
YOU WERE NOT THE FIRST PEOPLE TO FIND IT.
Kang took the paper.
He unfolded it.
There were three lines.
17 APRIL 1992
17 APRIL 2008
17 APRIL 2026
Kang frowned.
"That's today."
Hae-in looked at the dates.
Every sixteen years.
She reached for the file.
"Why 2008?"
Kang searched the detention center records.
"Renovation."
"What happened during the renovation?"
"I'll find out."
He typed.
Then stopped.
"There was a structural incident."
"What kind?"
"Worker injured during demolition."
"Name?"
He opened the report.
"Kim Seong-hwan."
Hae-in leaned closer.
"Dead?"
"No."
"Where is he now?"
Kang searched again.
His fingers stopped.
"He disappeared."
"When?"
"Three days after the accident."
Hae-in stared at him.
"From where?"
"Hospital."
She leaned back.
The room became quiet.
Not because the discovery was shocking.
Because it fit too neatly.
Lee Ji-hoon.
Kim Seong-hwan.
The current investigation.
Three dates.
Three people connected to the same building.
But something bothered her.
"Sixteen years."
Kang looked at her.
"Yes."
"Why?"
"I don't know."
"Neither do I."
She looked at the paper again.
The handwriting was different from the writing on the maintenance documents.
Different from the notes in Soo-jin's notebook.
Different from the message on the envelope.
Three dates.
Nothing else.
Hae-in turned the paper over.
Blank.
She looked at the photograph again.
Something about it bothered her.
The angle.
The height.
The photographer had been standing just outside the hidden room.
Almost exactly where Hae-in had stood.
She zoomed in on the image.
The chair.
The wall.
The table.
Then she saw it.
A small object beneath the chair.
She enlarged the photograph.
Kang leaned over.
"What is that?"
"I don't know."
It was a dark rectangle.
Half-hidden by the chair leg.
Hae-in pulled the original photograph from the evidence bag.
She compared it.
The object wasn't there.
She checked the hidden room again.
The chair was now against the table.
The floor beneath it was empty.
"Someone removed it."
Kang looked at her.
"After taking the photograph."
"Or before."
He stood.
"We need to go back."
They returned to Cell Block C with an evidence technician.
The hidden room was photographed from every angle.
The technician checked the chair.
Nothing.
The table.
Nothing.
The floor.
Nothing.
Then Hae-in noticed a shallow mark underneath the table.
She crouched.
There was a screw embedded in the floor.
Not a screw.
A mounting bolt.
She looked at the photograph again.
The dark rectangle beneath the chair was positioned directly beside it.
"Kang."
He crouched beside her.
"What?"
"This table used to be somewhere else."
"How do you know?"
"The bolt."
He looked at the floor.
"There are two."
The second hole was filled with dust.
Hae-in measured the distance.
"Someone moved the table."
Kang looked at the photograph.
"And the photograph was taken before it was moved."
"Yes."
"Why?"
Hae-in looked at the empty space beneath the chair.
"To hide what was under it."
The technician carefully lifted the chair.
Nothing.
Then they moved the table.
A thin metal panel appeared beneath one of the legs.
Kang stared.
"Another compartment."
Hae-in didn't answer.
The panel had no handle.
She examined the edges.
Someone had sealed it with paint.
Old paint.
But the center had been scratched recently.
She took a blade from the technician.
Carefully, she cut through the paint.
The panel lifted.
Inside was a narrow cavity.
There was no file.
No photograph.
No key.
Only a cassette tape.
Kang looked at it.
"Seriously?"
Hae-in picked it up.
A label was attached.
Handwritten.
FOR THE PERSON WHO ASKS WHY.
Kang sighed.
"Of course."
Hae-in looked at the tape.
Then at the hidden room.
"Don't play it here."
"Why?"
"Because if someone can control the cameras, they can control the room."
She slipped the cassette into an evidence bag.
"We listen somewhere they can't watch us."
At 4:18 that afternoon, they were back in Hae-in's office.
The old cassette player came from the evidence department.
It took three attempts to get it working.
The tape hissed.
Static filled the room.
Then a voice.
Male.
Older.
Calm.
Not distorted.
Hae-in and Kang looked at each other.
The voice spoke.
"If you found this, then the room survived."
A pause.
"That's unfortunate."
Kang leaned forward.
The recording continued.
"The people who built the system believed records were the weakness."
A click.
"They were wrong."
Another pause.
"Records are not the weakness."
Hae-in's eyes stayed on the recorder.
"Memory is."
The tape hissed.
Then the voice said:
"Lee Ji-hoon remembered the second door."
Hae-in's hand stopped above her notebook.
"Kim Seong-hwan remembered the second door."
A pause.
"Your father remembered the second door."
Kang looked at her.
Hae-in didn't move.
The voice continued.
"They all made the same mistake."
Static.
"They wrote it down."
The tape stopped.
Kang reached for the machine.
"That's it?"
Hae-in held up her hand.
"Wait."
The tape began again.
But this time, there was no voice.
Just footsteps.
One.
Two.
Three.
Then a door opening.
Someone breathing.
And finally—
A woman's voice.
Very quiet.
"Seo Hae-in."
Hae-in went still.
The recording ended.
The machine clicked.
Silence returned.
Kang stared at her.
"How did they know your name?"
Hae-in looked at the cassette.
She didn't answer immediately.
Then she reached for her phone.
"Check the recording date."
Kang looked confused.
"The cassette?"
"Yes."
"There isn't one."
"There has to be."
He turned the cassette over.
Nothing.
Then he noticed a tiny number written inside the plastic edge.
32.
Hae-in looked at it.
Chapter thirty-two.
Not a date.
Not a room number.
A chapter.
A sequence.
Someone wasn't merely leaving evidence.
They were counting.
Hae-in stood.
"We need to find out who recorded this."
Kang nodded.
"And how long they've been waiting for us."
She picked up the evidence bag containing the brass key.
08.
Then the cassette.
32.
Two numbers.
One unanswered question.
The Eighth.
And whoever had decided that Hae-in was next.