]
The photograph stayed on Seo Hae-in's desk all night.
She had turned it facedown.
It hadn't helped.
At 7:14 the next morning, she turned it over again.
The little girl smiled from the faded paper as though nothing in the world had ever been wrong.
Hae-in studied the photograph.
Then the message written on its back.
...don't let them...
Three words.
Not enough to solve anything.
Enough to make her uncomfortable.
She reached for her phone.
"Kang."
He answered on the second ring.
"You're awake."
"I assume you are too."
"I've been awake since five."
"Good. Meet me at the office."
A pause.
"Something happened?"
"No."
She looked at the photograph.
"Something didn't."
Kang arrived twenty minutes later.
He placed a file on her desk.
"Autopsy report."
Hae-in looked at it.
"Already?"
"The hospital moved quickly after we pushed."
She opened it.
The unidentified man's death had been classified as cardiac arrest.
No obvious poisoning.
No trauma.
No conventional cause of death.
But one line had been highlighted.
Unusual neurological activity immediately preceding cardiac event.
Hae-in read it twice.
"How unusual?"
"Enough for the pathologist to recommend further examination."
"Which means?"
"Someone told him to stop."
Her eyes lifted.
"Who?"
"Hospital administration."
"On whose authority?"
Kang didn't answer immediately.
He placed another document beside the autopsy.
An authorization form.
The signature at the bottom belonged to a senior hospital administrator.
Hae-in read the name.
Then looked at Kang.
"Do you know him?"
"No."
"Find out who does."
By noon, the answer arrived.
Kang stood in the doorway.
"The administrator isn't connected to the detention center."
Hae-in continued reading.
"But?"
"He worked for a private medical research foundation before moving into hospital administration."
"Which one?"
He handed her a second page.
She read the name.
Hanseong Neurobehavioral Research Foundation.
The words meant nothing to her.
Until she reached the attached employment history.
Her eyes stopped.
"How long did he work there?"
"Seven years."
"Doing what?"
"Behavioral research."
She closed the file.
"Get me everything."
The foundation's public records were disappointingly clean.
Charitable donations.
Academic partnerships.
Research grants.
Published papers.
Awards.
Nothing criminal.
Nothing suspicious.
Nothing that could survive a courtroom.
Hae-in hated clean records.
Not because they proved guilt.
Because sometimes they proved how carefully someone had prepared.
Kang sat opposite her.
"We can't accuse a foundation because one hospital administrator used to work there."
"I know."
"We don't even know if the foundation is involved."
"I know."
"Then what are we looking for?"
Hae-in leaned back.
"The daughter."
Kang went quiet.
She turned the photograph toward him.
"The original case has always been about what happened to her."
"We know that."
"No."
Her finger rested on the girl's photograph.
"We know how she died."
She moved her finger to the photograph.
"We don't know what happened before."
Kang stared at her.
"You think her death wasn't the beginning."
"I think we've been treating it like it was."
They returned to the evidence room that afternoon.
The daughter's belongings had been catalogued months earlier.
Clothing.
School materials.
A backpack.
A phone.
Several photographs.
Most had already been examined.
Hae-in requested everything again.
Not because she expected something new.
Because sometimes evidence became meaningful only after you knew what to look for.
The evidence technician opened the storage container.
One item was missing.
"The phone?" Hae-in asked.
"Already with digital forensics."
"The school records?"
"Returned to the family."
"The photographs?"
"Here."
She looked through them.
Birthday parties.
School events.
Family dinners.
Ordinary moments.
Then she found one.
The daughter standing beside a school building.
A group of students behind her.
Hae-in looked closer.
Someone had been standing at the edge of the frame.
Partially hidden.
A woman.
Black coat.
Face turned away.
Kang leaned over her shoulder.
"Can you identify her?"
"No."
Hae-in turned the photograph over.
Nothing.
She looked at the date.
Three weeks before the murder.
"Where was this taken?"
"The school," Kang said.
"I know."
She pointed at the building.
"Which part?"
He checked the school map.
"Old science wing."
"Is it still in use?"
"No."
"Why?"
Kang looked at the map.
Then at her.
"It was closed five years ago."
Hae-in's expression changed slightly.
"Five years?"
"Electrical problems. They renovated the building and moved the science classes."
She looked back at the photograph.
The woman in black stood beside the entrance.
Waiting.
Or watching.
They couldn't tell which.
The school was almost empty when they arrived.
Summer classes had ended for the day.
A security guard led them toward the old wing.
The corridor smelled of dust and old paint.
Most of the doors were locked.
At the end of the hallway stood a metal door marked:
AUTHORIZED PERSONNEL ONLY.
The guard unlocked it.
Inside was an abandoned laboratory.
Old desks.
Broken cabinets.
Dust-covered equipment.
Kang looked around.
"What are we supposed to find?"
"I don't know."
"That's reassuring."
She ignored him.
Her eyes moved across the room.
Nothing.
Then—
she noticed a small metal box beneath one of the desks.
Not old.
Clean.
Recently placed.
Kang crouched beside it.
"Don't touch it."
"I wasn't planning to."
Hae-in photographed it.
Then called the school's security office.
Twenty minutes later, they learned something that made the room feel smaller.
The box wasn't part of the school's equipment.
It had been placed there recently.
And the security cameras covering the corridor had been disconnected for exactly eleven minutes three weeks earlier.
The same day the photograph had been taken.
Hae-in looked at Kang.
"How long ago?"
"Three weeks before the murder."
The same date.
The same building.
The same unknown woman.
The same case.
Kang stared at the box.
"Do we open it?"
Hae-in shook her head.
"Not here."
Back at the office, the box was opened under controlled conditions.
Inside were three things.
A small digital recorder.
A key.
And a folded sheet of paper.
Hae-in opened the paper first.
There was no message.
Only a number.
17.
Kang looked at the recorder.
"Play it?"
She nodded.
Static filled the room.
Then a child's voice.
Faint.
Distorted.
But unmistakable.
Hae-in froze.
The daughter.
The recording lasted only nine seconds.
A few breaths.
A chair moving.
Then the girl's voice:
"She told me not to remember."
The recording ended.
Neither of them spoke.
Kang looked at Hae-in.
"That's impossible."
"No."
She stared at the recorder.
"It's evidence."
The key lay beside it.
Small.
Metal.
Stamped with the number 17.
Hae-in picked it up carefully.
She looked at the paper again.
17.
A room.
A locker.
A drawer.
Something.
They didn't know yet.
But for the first time since the case began—
the daughter had left them something herself.
Not a memory.
Not a clue someone else had interpreted.
A message.
And whoever had wanted her forgotten...
had failed.
Hae-in closed her hand around the key.
"We're going back to the school."
Kang stood.
"Tonight?"
She looked toward the dark window.
"No."
A pause.
"Tomorrow."
Kang frowned.
"Why wait?"
Hae-in's eyes returned to the photograph.
"Because if someone left this for us..."
She turned it over.
"...they may be waiting for us to find it."
The office fell silent.
For once, neither of them moved.
Because the investigation had just changed.
They weren't only searching for what had happened to the daughter anymore.
They were following the trail she had deliberately left behind.
And somewhere—
someone else was following them.