The apartment on Steiner Street had a view of the bay. Not a good view—the building was old and the window was small and a fire escape blocked part of the glass—but a view nonetheless, a rectangle of gray water and gray sky that changed color depending on the hour and the fog and the particular quality of San Francisco light that photographers crossed continents to capture.

Ed Morgan had been sitting at that window on the morning of June 12th, 1951, looking at nothing. He had a cup of coffee going cold in his hand and a stack of mathematics journals on the table that he had been meaning to read for three weeks and a feeling in his chest that he could not name—a restlessness, a sense of being held in place by something he could not see. He was twenty-eight years old. He had a degree from Berkeley. He had a life that was safe, insofar as lives were safe for a gay man in San Francisco in 1951, which was to say: not very safe at all, but manageable, discreet, livable.

He had been living in that apartment for two years. Before that, he had been in graduate school. Before that, the war, and before the war, a childhood in Berkeley that felt now like something that had happened to someone else—a different Ed Morgan, a boy who had not yet understood what he was or what it would cost him.

The coffee was cold. He drank it anyway.

The bookshop on Fillmore Street was where Ed worked three mornings a week, doing accounts for the owner—a widowed woman named Mrs. Kessler who didn't ask questions and didn't care that her accountant was sometimes seen at the bar on Ellis Street on Friday nights. The work was simple: invoices, receipts, the quarterly taxes that Mrs. Kessler paid with a scowl and a check. It paid almost nothing, but it gave him an excuse to be out of the apartment, to be doing something, to be part of the world even when he didn't feel like he was part of anything.

The afternoon of June 12th, he had gone to the bookshop to settle the accounts. Mrs. Kessler had been in a mood—something about a shipment of books that had arrived damaged—and Ed had spent two hours placating her and recalculating figures and pretending to care about the difference between retail and wholesale pricing. When he was done, he had walked out the back door into the alley behind the shop to smoke a cigarette, because Mrs. Kessler did not allow smoking inside, and because the alley was quiet, and because he needed a few minutes to himself before he walked home through the city he had lived in for three years and still did not feel like he belonged to.

That was when he saw the shimmer.

The alley behind the bookshop on Fillmore Street smelled of wet cardboard and diesel. It was a narrow space between the back of the shop and the wall of the adjacent building, paved with asphalt that was cracked and patched and stained with oil. There was a dumpster, and a stack of wooden pallets, and a fire escape that descended from the upper floors of the shop building and ended two stories above the alley floor, its rusted railings looking like the bones of something that had once been alive.

Ed had stood there many times. He had smoked dozens of cigarettes in that alley, watching the light change on the buildings across the street, listening to the sounds of the city—traffic, voices, the distant clang of the cable car on the hill above. He knew the alley the way you know a room you visit often: by its smells, its angles, the way the light fell at different hours.

But on June 12th, the alley was different.

The air was moving. Not wind—wind had a direction, a purpose, a reason. This was different. This was the air itself thickening, concentrating, as if the alley had become the center of something that was pulling the atmosphere toward it like a drain pulling water. The temperature dropped. Ed could feel it on his skin—the sudden chill, the wrongness of it, like stepping into a cold room on a hot day.

And there was light. A shimmer, faint at first, like heat rising off asphalt in August except it was sixty degrees and the alley was in shadow. But as Ed watched, the shimmer deepened. It took on texture, weight, dimension. It became a vertical slit in the air itself, perhaps two feet tall and a foot wide, positioned in the middle of the alley between the dumpster and the fire escape, and it hummed—a sound Ed felt in his teeth more than heard, a frequency that seemed to come from everywhere and nowhere at once.

The edges of the crack were not clean. They rippled. They looked like water—except water didn't stand upright in a rectangle, didn't hold its shape in defiance of gravity, didn't shimmer with colors that weren't colors, hues that seemed to exist just beyond the edge of the visible spectrum.

Ed dropped his cigarette.

He should have walked away. He knew this. He knew that what he was seeing was not possible, was not real, was not the kind of thing that happened to rational men who believed in mathematics and logic and the order of the universe. He should have gone back inside, finished his work, walked home, forgotten the whole thing.

But Ed Morgan had spent his whole life being careful. Careful about where he went, who he talked to, what he said, how he lived. He had been careful because carelessness was dangerous for men like him, because the world had rules about men like him that were enforced with jail cells and violence and the particular cruelty of people who believed they were righteous. And all that carefulness had kept him alive, but it had also kept him small. It had kept him contained.

He was tired of being contained.

He reached out.

His fingers crossed the threshold first. The sensation was extraordinary—not cold exactly, not hot, but a kind of absence of temperature, a nothing that nonetheless had texture, had presence, had weight. On the other side, he felt something he could not name: a space that was not space, a place that was not a place, a darkness that was not darkness but something else, something that existed between the place he knew and the place he was about to go.

And then the crack widened, or he fell forward, or both—the distinction did not matter, because what happened next was not something that happened in steps or stages but all at once, a single instant of transition in which the alley behind the bookshop on Fillmore Street dissolved and was replaced by something else entirely.

He fell.

There was no wind. No sense of descent, of falling through space, of the stomach-dropping lurch that accompanied ordinary falls from ordinary heights. There was only the sensation of movement—of being pulled or pushed or carried through something that was not quite matter and not quite light—and then, with an abruptness that drove the breath from his lungs and the thoughts from his head, there was ground.

Hard. Immediate. Real. He was on his hands and knees on cobblestones, and the impact drove pain up through his palms and into his wrists, and for a moment he could not breathe, could not think, could do nothing but kneel there on the wet stone and try to remember how his body worked.

The air was different.

He knew this before he opened his eyes. He knew it the way you know the difference between a dream and waking—not by the evidence of the senses but by the feeling, the texture, the particular quality of existence. The air in San Francisco smelled of fog and salt and diesel and the mustiness of old buildings with bad ventilation. This air smelled of coal smoke and wet stone and something else, something organic and distant, like a river that had not been clean in a hundred years.

Ed opened his eyes.

He was in an alley. But it was not the alley behind the bookshop on Fillmore Street. The cobblestones were older, darker, slick with moisture that had the quality of permanence, as if they had been wet for so long they had forgotten what it felt like to be dry. The buildings on either side were brick, soot-stained, four and five stories tall, with windows that were tall and narrow and dark. The fire escapes were wrought iron, not rusted chain-link—they were decorative in a way that spoke of another century, another city, another world. There was a lamppost at the end of the alley, and the light it cast was not the white glare of an electric bulb but a softer, yellower glow that flickered slightly, that had the warmth and imprecision of gas.

The sky above was a pale yellow-gray, the color of dishwater. Ed looked up and saw clouds—low, heavy, the kind of clouds that promised rain without guaranteeing it—and the space between the buildings was too narrow, too tall, too dark to give any sense of the larger sky beyond.

He stood. His glasses were askew. He straightened them and looked around and understood, with the slow, sick clarity of a man realizing he has misread a problem entirely, that he was not in San Francisco.

The street at the end of the alley said, on a green sign with white enamel letters that were worn by weather and age: Middlesex Street.

He had never heard of Middlesex Street. He had never seen a street sign like this, with this font, this material, this particular patina of age and use. He had never stood in an alley that felt like this—like stepping into a photograph from another era, into a world that was similar enough to his own to be recognizable but different enough to be wrong.

Ed walked to the end of the alley. His legs were shaking. His hands were shaking. He was not afraid—not yet, not fully—but he was close to it, balanced on the edge of something vast and incomprehensible, and he knew that if he fell over that edge, he would not be able to climb back.

The street was narrow, lined with market stalls that were closing for the day. He could see the signs of the closing: costermongers packing crates of apples and bundles of kindling, a man with a handcart full of kippers loading his last catch, a woman in a dark coat tending a brazier where chestnuts roasted and sizzled. The light was failing—it was evening, he realized, though he had left the bookshop in the late afternoon, and the change in the quality of the light was wrong, was too fast, was another evidence of the wrongness of everything.

The people on the street looked at him. Not with surprise—Londoners, he would learn, did not waste their surprise on strangers—but with the flat, incurious gaze of people who had seen everything and were not about to be surprised by a disheveled American in a sport coat. A woman in a hat walked past without turning her head. A boy in a cap shouted something to a friend across the street. An old man with a newspaper under his arm moved at the slow, certain pace of a man who had walked these streets for decades and had no intention of stopping now.

Ed opened his mouth and closed it. His cigarette had been in his hand when he fell. He could still feel the ghost of it between his fingers—the ghost of a habit he was trying to quit and failing at, the ghost of a life that had existed thirty seconds ago and no longer existed at all.

He reached into his jacket pocket for his wallet. It was there. He could feel the leather, the cards inside—the California driver's license with his photograph and his name and the address on Steiner Street, the union cards from the hotels where he'd done part-time accounting work, the three dollars in cash that he had been planning to use for groceries. He was himself. He had not dreamed his way here. The wallet was proof of that, was proof of continuity, was proof that whatever had happened was real and not the product of a fever or a breakdown or a psychotic episode that he would wake from in his apartment on Steiner Street with the taste of cold coffee in his mouth.

But the alley was gone. The crack was gone. The shimmer, the hum, the cold pull—all of it gone, as completely as if it had never been.

A woman with a pushcart turned the corner and stopped when she saw him standing at the mouth of the alley in a daze. She was perhaps fifty, with a face that was weathered and watchful, and she looked at him the way Londoners looked at things: flatly, measuring, deciding.

"You all right, love?" she said.

Ed's voice came out in a voice he didn't recognize—hoarse, scraped thin, as if he had been screaming. "I'm fine."

"You look lost."

"I am," Ed said. "I think I am."

The woman shrugged—Londoners had seen everything, had seen lost men and lost women and lost Americans who wandered into the wrong part of the city at the wrong time of day—and she moved on, pushing her cart around the corner and disappearing into the evening.

Ed stood in the alley mouth for a long time. The light was failing. The market was closing. Someone lit a lamp in a window across the street, and the flame was gas—steady, pale blue, flickering slightly in a draft that came from somewhere he couldn't see—and Ed watched it like it was the most important thing he would ever see, because it was the only thing in this new world that he understood. Gas lamps were old. Gas lamps were from another era. Gas lamps meant that this was not San Francisco in 1951 and was not any San Francisco he had ever known or would ever know.

He had no papers that mattered. He had no explanation. He had a worn copy of On Computable Numbers in his jacket pocket—he reached for it automatically, the way a man reaches for a rosary, the way a man reaches for the thing that has always been there when he needed it—and when his fingers touched the worn card cover, he felt something settle in his chest. Not calm. Not hope. Just the memory of certainty, of a world where problems had solutions, where the universe operated according to rules that could be understood and stated and proven.

He was standing in a city he did not know. He was standing in a country he did not live in. And the year was not 1951.

It was 1951.

He knew this not because anyone had told him but because the evidence was everywhere, accumulating in his mind like data points in a proof—the cars that were old, the lamps that were gas, the clothes that people wore, the particular quality of the air that spoke of coal fires and horse manure and a city that had not yet been rebuilt from the bombs of a war that had ended six years ago. He had fallen through something—a crack in reality, a tear in the fabric of space and time, whatever you wanted to call it—and he had arrived where he had arrived, and there was no equation for this. No proof. No logic that could explain why an American mathematician was standing in a London alley on a Tuesday evening in June with nothing but his wallet and a paper he already knew by heart and a feeling in his chest that was rapidly becoming fear.

The market stalls were empty now. The costermongers had gone. The street was quiet except for the distant sound of a bus—a proper red double-decker, moving slow, its headlights just starting to glow against the gray—and Ed watched it pass and thought: I am in London. I am in England. I am on the other side of the world from everything I know, and I don't know how I got here, and I don't know how to get back.

He did not cry. He was not yet at the point where crying was possible. He was still too busy being afraid, too busy trying to understand, too busy standing at the edge of the abyss and looking down into it and trying to calculate whether the fall would kill him or not.

A man walked past on the opposite pavement—well-dressed, middle-aged, carrying a briefcase—and he glanced at Ed with the automatic, dismissive attention of a man who had seen a dozen strangers that day and would forget all of them by morning. Ed watched him go and thought: that man has a life. That man knows where he is going and why. That man belongs here in a way that I do not.

And then, with a clarity that came from nowhere and everywhere: I have to find a place to sleep. I have to find food. I have to figure out how to survive in a city where I know no one and no one knows me.

He could not think about the crack in the alley. He could not think about how to get home. He could only think about the next step, the immediate next step, the thing that had to be done before anything else could be done.

Ed Morgan, twenty-eight years old, stood at the edge of everything he knew, and he began to walk.

He did not go home, because there was no home to go to. He walked into the London evening, into the gaslight and the fog and the narrow streets that smelled of coal smoke and wet stone, and he did not look back.