The seat assignment said 34A.

Sicheng had checked it three times on his phone before boarding, not because he'd forgotten, but because checking things was what he did when his mind needed somewhere to be. Taipei had been four days of his mother's cooking and his father's pointed silences and his younger sister asking questions he didn't know how to answer anymore. Four days of being someone's son instead of someone's researcher. He was ready to be the latter again.

He settled into the window seat with the efficiency of a man who had made this journey enough times that it required no thought. Laptop positioned. Noise-cancelling headphones around his neck, not yet on — he'd learned to wait until boarding was complete before sealing himself off. Too many times he'd missed his row being called, or a flight attendant asking him something important, or—

He opened the paper he'd been meaning to finish since Thursday. Reread the abstract. Read it again.

The words weren't landing.

Taipei did that to him. Sent him back to Edinburgh slightly unmoored, like a ship that had drifted from its anchor point and needed time to find true north again. It would pass. It always passed somewhere over the Bay of Bengal, when the cabin went dark and there was nothing left to do but think about the work waiting for him.

He was on the second page of the methodology section when the aisle seat beside him filled.

He didn't look up. He never looked up during boarding — it invited conversation, and conversation on long-haul flights was a particular kind of exhausting he preferred to avoid. He registered the presence peripherally: a carry-on being lifted into the overhead bin, the soft percussion of someone settling in, the click of a seatbelt.

Then a voice, low and directed at the flight attendant passing in the aisle.

"请问这个座位可以调整靠背吗？"

His eyes stopped moving across the page.

It wasn't the Mandarin. There were always Mandarin speakers on flights out of Taipei. It was something else — a particular cadence, a specific way the question curved at the end, not quite Taiwanese, not quite Beijing, something in between that he had only ever heard from one person.

He looked up.

The recognition didn't come all at once. It arrived in pieces, the way it does when you see someone outside the context where they exist in your memory. First: a profile. The line of a jaw, the way dark hair was tucked behind one ear. Then: the hands, folding a boarding pass with the precise, habitual movements of someone who needed something to do with their fingers. Then: the particular way she turned her head when the flight attendant responded, a slight tilt that was entirely, unmistakably—

Song Yutong.

Four years.

He had not seen her in four years, and she was sitting in seat 34B.

His hand moved to his left wrist before he'd made any conscious decision. Found the watch strap. Pressed down once, a small pressure, a small anchor. He was aware, with the detached clarity of someone watching themselves from a slight distance, that he had approximately three seconds before she finished speaking with the flight attendant and turned forward and saw him.

He could look down. Return to the paper. Let her see him already absorbed, already elsewhere, give them both the exit of pretending.

He didn't look down.

She turned.

The moment her eyes found him was like a held breath made visible. He watched the recognition move across her face — faster than his had been, or perhaps just less concealed — a slight stilling, a fractional widening, then nothing. Her expression didn't close exactly. It simply became careful.

"Lin Sicheng," she said.

Not a question. Not quite a greeting. His name in her mouth, stated like something being confirmed.

"Song Yutong." He heard himself match her register exactly — formal, even, giving nothing away. "Edinburgh?"

"Edinburgh," she said.

Four hours and twenty minutes remaining on the flight. He knew this without checking. He had memorized the schedule the way he memorized everything that mattered: thoroughly, automatically, against the possibility of needing it later.

He needed it now.

She reached under the seat for her bag and retrieved a book — not a tablet, an actual paperback, which he noted without intending to — and opened it to a bookmarked page. The message was clear and he received it without objection. He put his headphones on. Returned to the methodology section.

Read the same paragraph four times.

The problem was proximity. He was accustomed to managing the idea of Song Yutong from a distance of several thousand miles and four years of deliberate non-contact. That distance had made her manageable: a chapter of his life that was complete, if not entirely comfortable to revisit. But she was not several thousand miles away. She was eleven inches to his left, and he was aware of her the way you are aware of a sound you can't quite identify — not intrusively, but constantly, a frequency running beneath everything else.

He noticed when she shifted position. When she turned a page. When she accepted a glass of water from the flight attendant and set it on the tray table with a precision that was characteristic, that he recognized from memory without wanting to.

He focused on the paper.

The methodology section was actually quite good. He made himself care about this.

They were two hours into the flight when the meal service came, and the geometry of economy class made neutrality temporarily impossible. Tray tables down. Foil containers. The small, enforced intimacy of shared armrest space.

"Which program?" he asked.

He hadn't decided to ask. It had simply emerged, in the way that silence sometimes becomes its own kind of pressure.

She looked up from her tray. "Computational biology. You're still in the Henderson lab?"

"Fourth year."

"Finishing?"

"End of this academic year, if the data cooperates."

A faint curve at the corner of her mouth. Not quite a smile. An acknowledgment. "It rarely does."

"No," he agreed. "It doesn't."

They ate in a silence that was different from the previous silence — less deliberate, less armored. He found himself noticing that she ate the way she'd always eaten, starting with whatever she liked least and working toward what she wanted, as if pleasure had to be earned in the correct order. He didn't know why he remembered this. He remembered it anyway.

"The Whitmore group?" he asked, because he knew the computational biology labs at Edinburgh, and he knew which one would take a researcher of her profile, and asking was better than already knowing.

She looked at him briefly. "You follow their work?"

"Adjacent field. Some overlap." A pause. "Their methodology has improved significantly in the last two years."

"I know," she said. "I wrote two of those papers."

He had known this too. He hadn't known that he'd known it until she said it, and then it was obvious — of course he had encountered her name in the literature, of course he had read her work with the particular attention you give to writing that is doing something interesting, and filed it somewhere he didn't examine too closely.

"They're good papers," he said.

"Thank you." Precise. Not warm, not cold. Receiving a professional assessment professionally.

He wanted, suddenly and inconveniently, to say something that wasn't professional. He didn't. He returned to his meal, and she returned to hers, and the conversation ended as cleanly as it had begun.

She asked him nothing about Taipei. He asked her nothing about where she'd been. The four years between them sat in the eleven inches between their seats, present and unaddressed, and he found that this was almost manageable. Almost.

The lights went down an hour later. The cabin settled into its nighttime configuration — blankets, eye masks, the particular hush of two hundred people collectively agreeing to pretend they were elsewhere. He angled his seat back the permitted amount and closed his laptop.

Beside him, she had gone still. Eyes closed. Breathing slow and even, or slow and even enough that it didn't matter whether she was actually asleep.

He did not sleep.

He looked at the dark window and thought, with the methodical honesty that nighttime tends to permit, about the Edinburgh he was returning to. He had built it carefully over four years. He knew its rhythms: the particular gray of November mornings, the way the Old Town looked from the Meadows on clear days, the Henderson lab at 11pm when everyone else had gone home and the work became simple again, just him and the data and the clean quiet of knowing what he was there for.

He had built that Edinburgh without her in it.

It had not occurred to him to do otherwise. She had been in Shenzhen, or Beijing, or wherever the work had taken her — somewhere on the other side of a distance he had, over time, stopped measuring. And now she was in seat 34B, and in approximately ninety minutes she would be in Edinburgh, and the Edinburgh he had built would need to be rebuilt around a new variable.

He was good at variables. This was, technically, just another one.

He told himself this with the conviction of a man who had spent four years being very good at telling himself things.

The descent announcement came. Cabin lights up, tray tables stowed, the mechanical preparations for arrival. Beside him, she straightened — awake, or done pretending — and gathered her things with the same efficient precision she'd used to settle in. He did the same. They moved through the routine of landing in parallel, without speaking, without the need to.

At baggage claim he found his suitcase quickly. She was still waiting when he turned to go, watching the carousel with the focused patience of someone who had learned that waiting was simply a thing you did.

"Yutong."

She looked at him. He wasn't sure why he'd said her name — her given name, not her family name, which was what they'd been using all flight, and the shift was small but not nothing.

He hadn't planned what came after it.

"The Whitmore lab is good," he said finally. "You'll — it suits your work."

A beat. She looked at him in a way that was difficult to read, and he had always found her difficult to read, even when they were close enough that he should have been better at it.

"Edinburgh is smaller than people expect," she said. Not to him, exactly. Almost to herself. "Everyone says that about it."

Her suitcase appeared on the carousel. She lifted it with both hands, extended the handle, and walked toward the exit without looking back.

He stood at baggage claim with the particular stillness of a man replaying a sentence he doesn't entirely understand.

Edinburgh is smaller than people expect.

He thought about it on the taxi into the city, the dark hills rising around them, the first lights of Edinburgh beginning to appear through the rain-streaked window. He thought about what she meant, or what she might have meant, or whether she had meant anything at all and he was simply doing what he always did — looking for precision in things that weren't meant to be precise.

He looked at the city coming toward him.

Four years ago he had made a choice, or failed to make one, which amounted to the same thing. He had told himself at the time that it was the right thing. He had told himself this with enough consistency that it had become, if not true, then at least familiar.

She was going to be in Edinburgh.

He watched the castle emerge from the dark above the city, lit against a sky that was just beginning to lighten at the edges, and thought: this time will be different.

He wasn't sure yet whether that was a hope or a warning.