Walk north. That was the only plan he had, and it was substandard.

Ed moved out of Middlesex Street against the flow of evening traffic—a woman in a green coat, a boy with a satchel, a man whose face was already forgetting him—and he walked because walking was the one thing his body still knew how to do without permission. His legs worked. His lungs worked. Everything else had stopped and he was not sure it would start again.

The city unfolded around him in pieces he couldn't assemble. The City of London came first: canyons of dark stone and narrow streets where the traffic thinned and the lamps were sparse and the shadows had settled in like permanent tenants. Above him, the buildings leaned together at upper floors, blocking the sky, so that the street felt less like a thoroughfare and more like a wound in the earth. The cobblestones were uneven, polished smooth by a century of cart wheels and polished smoother by the rain that had fallen an hour ago and left the surface dark and treacherous. He smelled coal smoke and something else—fish, maybe, from a shop he couldn't see—and the particular damp mineral scent of a city that had been old before his grandfather was born.

Then Clerkenwell, where the pubs lit up and men stood outside in clusters, smoking, talking in voices Ed had to strain to understand. Not the words—the words were English. The accent was a foreign country.

He was the foreign country now.

Ed had never been east of Chicago. He was California-born, Berkeley-educated, and he had built his adult life in the cramped, careful world of San Francisco's gay bars and church-basement meetings—living under a law that could destroy him but rarely bothered to, because he was white and middle-class and knew how to disappear. He thought he understood what it meant to be hunted. He knew the particular chill of seeing a policeman's badge in a bar window, the way a room could go quiet in half a second, the calculus of exit routes that every gay man in America learned before he learned to drive. He knew the fear that lived in the chest and the stomach and the backs of the knees—the constant low-grade terror that was so familiar it had become almost invisible, like a noise you'd stopped hearing because it never stopped.

London hunted differently. London hunted with paperwork.

He walked until he reached a wide avenue he didn't recognize, flanked by a stone arch and traffic that moved in the wrong direction. He stopped at the crossing and waited for the lights to change, then realized there were no lights—only a policeman on a box in the center of the intersection, raising and lowering his hand in a rhythm that seemed personal, almost musical, a gesture that assumed everyone watching understood the language it spoke. Ed did not understand. He crossed anyway, when the man lowered his hand, and felt the nudge of a woman with parcels against his shoulder as they both moved forward, and felt, for the first time since the alley, the sensation of being a body in a city rather than a mind in crisis.

He had no pounds. He had no address. He had no passport, no record, no place in any database the British government maintained. His California driver's license was a curiosity. His union cards were meaningless. He had three dollars in cash, which at the exchange rate came to roughly one and a half pounds—not enough for a room, not enough for a meal, not enough for anything except the immediate problem of not starving before morning.

He found a low stone wall bordering a dark patch of grass and sat. The stone was cold through his trousers. Above him, the trees were English trees—not the twisted pines and blue gums of California, but something denser, wetter, darker. The leaves were large and heavy with recent rain, and they moved in a wind he couldn't feel at ground level, stirring against each other with a sound like whispered secrets. A gas lamp nearby hissed and flickered, its flame uncertain, its light pooling yellow on the wet stone and the dark grass and his own hands, resting on his knees. He watched it like it was the only thing in this new world he understood. Gas lamps were old. Gas lamps meant 1951, or close enough, and that was close enough to be terrifying.

A bus passed, red and double-decker, its headlights just starting to glow in the dimming light. Ed watched it slide through the glow and thought: that man on the bus has a life. That man knows where he's going and why. That man has a bed to sleep in tonight and a drawer with his socks in it and a dentist he visits twice a year and a reason to set his alarm.

Ed didn't.

He sat until the dark was total. Then he got up and walked east—or what he thought was east—because sitting still felt like giving up. He crossed the Thames on a bridge he didn't know the name of, standing still on the walkway to watch the water: wide, black, moving slow, carrying the reflection of the lights on the south bank in long ribbons that stretched and broke and reformed as the current moved them. He could smell the river—something organic and deep, not unpleasant, just present, a reminder that the city sat on top of a living system it had spent centuries trying to control and had never quite managed. He was hungry. He hadn't eaten since morning, before the alley, before the crack, before the world split open and swallowed him whole.

He walked along the south bank until the streets turned residential—terraces and corner shops and pubs with names like The Angel and The White Lion, their windows glowing amber in the dark, the sound of voices and laughter and the clink of glasses spilling out onto the pavement whenever someone opened the door. He stopped at a shop window and saw his reflection: lean face, glasses slightly crooked, expression caught between lost and furious. He didn't recognize the man looking back. The shop sold hats. The hats were arranged on stands behind him, fedoras and bowlers and caps, and in the glass he looked like a man who had lost everything including his sense of humor, which was probably accurate.

A policeman turned the corner.

Ed saw the uniform before the man: the tall hat, the cape too heavy for June, the flashlight beam sweeping the pavement. His body went rigid. He had been followed out of a bar on Ellis Street once, in 1949, and had spent three blocks walking very fast and then diving into a cinema to hide. That fear was nothing compared to this. That fear had been about discretion. This fear had a specific, immediate object—the flashlight beam, the uniform, the authority that came with both.

The flashlight reached Ed's shoes.

"Mind your step, lad," the policeman said. His voice was ordinary—not cruel, not kind, just the voice of a man doing a job. Ed almost wept with relief at the sound of something so normal.

"Good evening," Ed said.

The policeman stopped. He was younger than Ed expected—maybe thirty—with a face that hadn't yet been worn down but was headed there. He looked at Ed's sport coat, the torn pocket, the American shoes. He looked at Ed's face.

"You're a long way from home," he said.

"I'm from San Francisco."

"California." Something shifted in his expression—not suspicion exactly, but attention. The attention of a man who had been trained to notice things that didn't fit. "What brings you to London, Mr. California?"

Ed opened his mouth. Closed it. He had no answer. He could not say: I fell through a crack in an alley. He could not say: I am a mathematician who has lost his entire life. He could not say: I have no papers because I did not travel here by any means that leaves a record.

"I came to—" he started.

"Could I see some identification, please?"

The question was polite. The question was standard. The question was a door opening onto everything Ed did not have.

"I don't have it with me," Ed said.

"Where are you staying?"

"I don't have a place to stay."

"And when did you arrive?"

"Today. Just today."

"Which boat did you come over on?"

Ed was silent.

The policeman watched him. Then he reached for a small notebook on his belt, took out a pencil, wrote something down. The pencil moved across the page with a soft scratching sound. Ed could see the policeman's hand—steady, professional, the hand of a man who had filled out a thousand of these forms and knew exactly how this one ended.

"I'm going to have to ask you to come with me," he said. "You'll have a warm cell for the night. In the morning, we can sort it out."

"I haven't done anything."

"No. But you can't account for yourself, and those are the regulations."

He was not cruel. That was the worst part. He was doing his job with the dull precision of machinery. The law was a machine, and Ed had fallen into its gears, and the machine was going to grind him no matter what he said. There was no malice in it. There was no interest. There was only the machine, grinding, moving forward, doing what machines do.

The policeman walked him to a call box—a glass box on a corner, warm light inside, nothing like the emergency phones Ed would have expected. He made a call in low, rapid murmurs, his breath fogging slightly in the cool evening air. Within twenty minutes a black Wolseley had arrived, government plates, and Ed was in the back seat between two men who said nothing and drove him north and east through streets he had no hope of recognizing. He pressed his forehead against the window and watched the city slide past—the dark masses of buildings, the occasional lit window, a child being put to bed in a room he would never see. He was being moved through London like a package, from one location to another, with no say in the routing.

The police station smelled of damp wool, disinfectant, and tea left too long in the pot. They took his wallet and belt and shoelaces. They gave him a receipt—a small blue form with his name misspelled and his belongings listed in a careful clerk's hand. They put him in a cell that was six feet by eight, with a straw mattress and a bucket and nothing else.

He sat on the mattress and listened to the sounds beyond the door—the muffled footsteps, a telephone ringing, keys scraping in locks. The cell was cold. The stone walls sweated with moisture, and the straw on the mattress was scratchy and smelled of other men, other nights, other crises that had ended up here before his. He could hear someone singing, faintly, from a cell down the corridor—a music hall song, half-remembered, the melody drifting through the stone like something from a dream.

He thought: this is the first day of the rest of my life.

He had not chosen it. But here he was.

He thought about Turing. The paper in his jacket pocket—confiscated, of course, locked in a drawer somewhere in this building, along with his belt and his shoelaces and his dignity—but he could see it in his mind. The theorems. The proofs. The leap of a man who had described a universal machine before the machine existed. The beautiful, impossible idea that a machine could compute anything that was computable, given the right instructions, given enough time.

Ed had read that paper in 1947, in a seminar at Berkeley, and had understood then that the most powerful things in the world were the ones you couldn't see. Ideas. Proofs. The structure of logic itself. These were the things that mattered—the architecture beneath the surface of everything, the invisible scaffolding that held the world together and made it comprehensible.

He was sitting in a cell in London with no papers and no money and no way home, and the most powerful thing he had was the memory of a paper that had changed his life.

It would have to be enough.

He lay back on the straw mattress and closed his eyes and did not sleep.