The conductor came down the aisle.

Not fast. It had never once been fast. White gloves at its sides, lever punch swinging loose in one hand, eggshell face catching the car lights and giving nothing back.

Click. Clack. Click.

Its shoes on the floor kept time like a metronome nobody wound.

Mu-hyeon stood up.

He didn't say anything. He just moved into the aisle, one hand on a strap, and became the widest thing in the car. Between the punch and the three of us, there was now a firefighter.

The conductor stopped one row short of him.

The punch rose. My whole spine went cold.

It came down on the headrest of an empty seat. Ka-chunk. A little paper crescent spun out of nothing and fell on the cushion.

Then it turned, walked back up the car, and took its post by the front doors. Facing us. Patient.

"Haa," Haru breathed out beside me. "Okay. I hate him. I've decided."

"You decided that an hour ago."

"I'm deciding it again, receipts. It holds."

Minseo hadn't sat back down.

She stood in the middle of the car with her dead phone in both hands, thumb moving over the black screen the way you'd rub a worry stone. Sixty-one percent, frozen forever under the glass. She'd told me once. I hadn't forgotten.

"Next one's mine," she said.

Nobody argued. The wall lights of the tunnel were already stretching, slowing, going from streaks back to dots.

Mu-hyeon didn't return to his old seat. He took the one nearest the conductor instead, aisle side, body angled out. The worst seat on the train, and he settled into it like it had his name on it.

The brakes sighed.

Tiles rose in the windows. White, old, grout gone gray. Blue letters.

MYODONG.

The slot in the conductor's face opened with a wet paper sound, and the canned announcer's voice came out, bright and dead.

"Now arriving, Cheonmun. Cheonmun station. The exit doors are on your right."

One ahead. The rule holding, sixth time in a row.

Myodong on the wall. Cheonmun in the air. Minseo's signal, exactly as we'd mapped it.

The doors opened.

Chime.

Warm air came in off the platform, and Minseo looked out at her station and did not move.

I saw what she was seeing. It wasn't hidden. The east stair, straight ahead across the platform, the same tile, the same bent handrail. A streetlight burning at the top of it, up in the world. Haedong General is a four minute walk from that exit. Night nurses take that stair because the west one floods.

"I've climbed that stair four hundred times," Minseo said. Her voice was even. That was the frightening part. "Clock in at nine. Ward six. Bed three used to ask me what I brought him."

Her thumb stopped moving on the phone.

"The last thing I did in that building was walk past a door and let it click shut."

Chime. The doors don't wait. Everyone in the car knew how long the chime lasted, down in our bones, because we'd counted it four times now with our hearts in our mouths.

She wasn't going to make it. She was going to stand there and the doors were going to close and the conductor was going to start walking.

Haru moved.

No speech. She just crossed the car, slipped her hand into Minseo's, laced the fingers like they'd done it a hundred times, and stepped toward the doors. And Minseo's feet, nurse's feet, feet that follow, followed.

One step. The threshold line, yellow and worn.

Haru stopped there. She didn't cross it. Her ticket said Cheonmun, not here; the door would take it and spend it and she knew that, and her toes stayed one centimeter on our side of the line while her arm went out over it, all the way, giving Minseo the whole length of her reach to walk down.

"Hey. Nurse unni."

Minseo looked back at her. Half in, half out. The chime ringing down.

"You're going up there to open a door you left shut," Haru said. "That's all. That's the whole mission. You're allowed a small thing."

She let go.

Minseo stepped down onto the platform of Myodong station, both feet, and the chime ended, and the doors began to slide.

She turned around.

Through the narrowing gap, dead phone against her chest, Joo Minseo looked at the three of us and said,

"I'll make the coffee."

The doors shut.

Through the glass I watched her stand there a second, small under the platform lights. Then she faced the east stair, squared up to it like it was a shift starting, and walked.

The train pulled out. She didn't watch us go. She was already climbing.

[A passenger has arrived.]

[Binding has been extended.]

[Remaining aboard: 3.]

"...Ha." Haru dropped into the seat across from me and put her face in her hands for exactly one breath. Then she came up grinning, chipped tooth and all, eyes wet. "She's going to make terrible coffee. Hospital people only know machine coffee. We're going to drink it and say it's great."

"We're going to say it's the best coffee in the city."

"Best coffee left in the city. Low bar. Still true."

The tunnel took us. The lights went back to streaks.

Three of us. Me, Haru, and Mu-hyeon in the worst seat, forearms on his knees, watching the conductor the way you watch a kettle you don't trust.

"Mu-hyeon-ssi." Haru tipped her head at him. "I've been keeping a list."

"Mm."

"Kindergarten. You stood at the door. Fire station, you sleep in the bunk by the stairs. This train, you've moved seats six times and every single time it's the one closest to that." She pointed her chin at the conductor. "I named the seat, by the way. It's called the worst seat. It's the only name it deserves."

"Somebody sits there," Mu-hyeon said.

"Why you, though."

He was quiet long enough that I thought that was the answer.

"My sister was loud," he said. "Louder than you, even."

"Impossible. But go on."

"When it happened, I was three streets away." He turned the axe handle a few degrees against the floor and looked at it. "Buying nothing. There was no seat that night. There wasn't even a room. So now, when there's a seat, I sit in it. That's all it is. It's not deep."

It was the most words I'd ever heard him spend on himself. My chest hurt in a way I didn't have anywhere to put.

Haru studied him. Nineteen years old, swinging her feet, holding a fireman three times her size in place with a look.

"Okay," she said. "But after this, you let somebody else stand in the doorway. Once. One time. As a treat."

"Noted."

"That's what you said to Baek-gu-ssi about sleeping."

"Mm."

"Do you know that word doesn't legally bind you to anything? I've checked."

Something happened at the corner of Mu-hyeon's mouth. On anyone else you would call it a smile starting. On him it was just weather.

And under the banter my brain kept doing what it does. Counting.

Baek-gu, off at Wonseo, whistling up the stairs. Chae-a at Haedong. Minseo at Myodong, climbing to her door.

Which meant the next station on the line was Cheonmun.

Mine. Haru's. Same stop, same ticket, same chime.

Two of us off, and then Mu-hyeon alone with the thing at the front of the car. My stomach dropped every time I got to that part of the count, so I stopped counting.

The motors changed pitch.

Already? Baek-gu would've known if the gap was wrong. Baek-gu wasn't here. I had nothing but a nurse's trick and a delivery man's clock, secondhand, and the brakes were sighing, and the tunnel lights were slowing into dots.

Haru stood. Checked her ticket. Looked at me.

"Together, right? Same chime."

"Same chime."

Tiles rose in the windows.

CHEONMUN.

And my whole body, every stupid trained nerve in it, said go. Because I'd heard that exact word an hour ago, out of the slot, and it had been Minseo's signal, the true one, the word that meant a person steps off and lives. Cheonmun means go. My ears had learned it like a bell.

No.

That was her signal. The name one ahead of her stop. Our signal is the next name up the line. Our signal is Hwagok. The wall means nothing, the wall is where we are, the wall said Saejae while the voice sang Daeheung. Rule five. It does not announce its stops truthfully.

The doors opened on Cheonmun station. Our station. The right tiles, the right name, warm air, an exit stair with dawn-gray light spilling down it.

Chime.

The conductor's slot stayed shut.

No voice. No name. Nothing but the chime running down, and our station standing wide open in front of us, and Haru's hand finding my sleeve, and the punch, somewhere up the car, going ka-chunk.