Seorin laid her palm against the wall.
She felt no vibration from the knocks. The sound rose from below rather than directly behind it. Doun bent a knee and listened near the floor too.
“Not straight through here.”
Caretaker Nam Gijun asked again over the phone.
“She seems to be looking for you. Do you know her?”
“Not yet. I’m calling for help first. Check that the exit by the office opens. From inside.”
She ended the call and contacted emergency services. Former Eundam Residence. Near the west-wing second floor. One adult woman visible on a monitor. Present location and condition unconfirmed. She separated what she knew from what she did not.
“While the team comes, we’ll locate the sound.”
The dispatcher told them to stay out of dangerous areas and remain in contact. Seorin added the location of the nearest way outside, then passed Doun the phone.
“Follow and take photographs. We stop if we reach an unstable floor.”
He nodded.
She also checked that wet patches did not meet electrical cables. Small discomforts in a corridor still needed an order of priority. A way to the person, a way back out, then an explanation. The unfamiliar use of her own name made her want to change that order. She steadied herself. Whether the person could hold on mattered before who was calling for her.
At the end of the corridor linking the wings stood a cleaning cupboard, holding three upturned mops. Dust lay unusually thick beneath it.
No. Not dust.
Crumbled rubber.
She crouched and shone the torch behind the cupboard. A small grille sat in the wall. One screw was missing; the cover stood loose. Cold air came through.
“The draught’s here.”
“An open space in the connecting section.”
Doun unfolded the plan again. Beneath the black line between the wings, part of a cropped dimension remained. Only the unit at its end was legible.
Millimeters.
Whoever had removed a real space from a printed page had failed to remove the end of its measurement.
Seorin knocked lightly with her knuckles.
Once. A pause. Twice.
After a moment, the same rhythm answered.
Doun spoke into the phone.
“We think there’s someone inside. Responding to knocks. We’re in front of the wall.”
Seorin brought her mouth close to the grille.
“I’m Lee Seorin, here for the safety inspection. I’ve requested rescue. Can you hear me?”
A cough came first. Then a small answer.
“Yes.”
She breathed out. A person in the present, beyond a screen.
“Are you hurt?”
“My ankle, a little. The door won’t open.”
“Can you breathe? Any burning smell?”
“No smell. It’s cold. I can hear water.”
She repeated the words to Doun, who repeated them into the phone. With each accurate passage from one person to another, fear became a little smaller.
“Where’s the entrance?”
“I came down from the east wing. Half a floor below the landing. Blue door.”
Seorin folded the plan. No such route appeared on it.
“Your name, please.”
“Baek Haeun.”
“Haeun. We’ll check the entrance. Doun will keep making a sound here so you—”
He looked at her. She had been the one to say they would stay together.
After a moment, she shook her head.
“No. We’ll go together. If we can’t find it, we’ll come back. If we do, we’ll call from the other side. Please stay back from the door.”
“I’ll wait.”
Quiet, but clear.
Seorin did not raise her voice further. Haeun need not spend her remaining strength answering. They agreed that two knocks from inside would mean danger. Seorin did not promise to keep speaking while they searched. She left only words she could keep and stood.
“First time along here?” Doun asked, matching her pace.
“First time in this building.”
“Must be irritating, coming in with a plan you trusted.”
“Plans can be wrong. Checking and correcting them is my job.”
“Would be good if people could be corrected.”
She looked at him, but he was checking the stairs. Instead of asking what he meant, she examined the connecting ceiling height. Between the west wing’s high floor and the east wing’s low ceiling, there was room for a half level missing from the drawing.
A blank you could find only by looking vertically.
They reached the east-wing stairs. The fire door opened from inside. The floor was dry, the railing firm. Four steps below the landing, a blue steel door appeared beside a gray wall.
A silver grille sat in its center.
Seorin looked down. A smooth threshold with a black rubber strip.
“Found it.”
No sign above the door, only old screw holes. It was secured by an external latch rather than a padlock.
A latch someone had to lower from outside.
Doun photographed the entire door and latch. Seorin asked after the person inside while lighting the doorway.
“Haeun. We’re at the blue door. The outside latch is down.”
A short breath came from within.
“It wasn’t locked when I tried to leave before.”
Seorin did not answer. Deciding who had locked it came later.
She updated the dispatcher and checked the floor outside for obstacles. After telling Haeun to keep clear, she lifted the latch with a gloved hand.
Metal rasped softly.
The door opened inward.
A woman sat in the torchlight. Gray work clothes. Dusty trainers. Crumpled white envelope.
The person from the screen looked up.
“You really came.”
Holding the door, Seorin checked inside. A low ceiling crossed by three pipes. Water pooled on part of the floor, short of their route.
“Can you stand?”
“Slowly.”
Doun reached from outside. Haeun braced against the wall and rose, then closed her eyes as she put weight on her right foot.
“Don’t force it. The rescue team’s coming.”
Seorin moved her bag aside and made a place to sit on the dry landing beyond the blue door. Doun guarded the latch from outside so it could not drop again.
Her phone rang. Gijun.
“The woman’s disappeared.”
Seorin looked at Haeun, who raised her head as though she had heard.
“We found her. East-wing connecting section.”
“No one’s on the screen now.”
“We met at 19:09. Your screen should show 18:56. She probably moved into the blind spot below the camera before that.”
Asked, Haeun nodded.
“I moved against the wall. I was cold.”
Gijun said nothing.
“Guide the rescue team here when they arrive. Leave the entry log where it is.”
She ended the call and turned to Haeun.
“May I ask why you put my name on the envelope?”
Haeun smoothed it open.
TO LEE SEORIN.
The name was written in thick black marker. Smaller words followed.
Please check the room missing from the register.
“Your work notice was at the front entrance. It said you were coming for a safety inspection.”
Seorin remembered the notice: time, name, company number. A stranger knowing her name did not always require a great secret.
“Did you try the company number?”
“Just a message saying the office was closed. I was going to leave my number, then I came inside. I thought the caretaker would stop me if he saw me.”
“Why?”
Haeun worried the envelope’s mouth.
“I kept asking him for names.”
“Whose?”
“People who used to live here.”
Inside were two photographs and a thin utility bill. Haeun began to take them out, then stopped. Her fingers shook.
Seorin did not take the envelope for her.
“We’ll look somewhere safe. Your ankle first.”
For the first time, Haeun looked close to crying. More than when the door had opened.
“Do you remember who passed you?”
“Navy work clothes. Looked at my envelope, then pretended not to see it.”
“A face?”
“The cap hid it. After they passed, the door shut. I heard it lock, but at first I thought it was the wind.”
Seorin checked whether she meant something seen or something concluded afterward. Haeun considered, then shook her head.
“I didn’t see the latch being lowered. Only heard it.”
That was no small difference.
Footsteps sounded above. Gijun led two rescue workers wearing fluorescent markings.
“Who called?”
Seorin raised her hand.
One introduced himself as Jeong Yunjae, then checked Haeun first. He asked about the rescue location, door fastening, and pooled water, recording the answers. Doun showed the door photographs.
“No one actually saw someone lock it?”
“Correct. We both saw the external latch down,” Seorin said.
Gijun spoke.
“That door is normally kept locked.”
Yunjae looked at him.
“With someone inside, using something that only opens from outside?”
Gijun closed his mouth.
Haeun went up with a rescue worker’s support. Seorin stepped aside, and removed her gloves only after watching the trapped woman reach the outside landing above.
Her palms were damp inside them.
Yunjae handed Doun barrier tape and told him not to touch the equipment cabinet. Seorin nodded. Opening a door to rescue someone differed from dismantling a device to investigate. With the rescue complete, she had to be the first to stop.
“Did you directly measure the thirteen-minute delay?”
“Compared the displayed time with my phone’s standard time twice. We haven’t done a timed test in this room yet.”
“Keep that distinction in the record.”
“Yes. The door and threshold establish that it shows another location.”
Reading her notes, he nodded once. Agreement with her distinctions, rather than her certainty.
She wrote the first line on the back of the plan.
PERSON FOUND ALIVE.
There was no NO OCCUPANTS REMAIN box beneath it. The person writing could make the fields herself. She added the time and an arrow toward the safe landing Haeun had reached.
Doun shone his torch above the blue door.
A camera. Small, white, rectangular. Entirely different from the black dome outside 214.
Its cable followed the ceiling corner into an equipment cabinet. A blue cable tie hung there, marked with a number in black pen.
780.
Seorin opened her phone calculator.
Seven hundred and eighty seconds made thirteen minutes.
Doun lowered his torch.
“That knot.”
His voice had changed slightly.
“I tied it.”