Assembly

Twenty months after a rocket in Chile did not fly, Mae Tsao walked onto the floor of the first factory in the world that built itself.

Fab 9 did not make chips. It made the arms that made chips, and on one line, at the back, it made more of its own arms. It worked in the dark. Robots did not need light, so there was none, and at half past three in the morning the ceiling woke above her one panel at a time and kept her in a moving pool of white, as if the building were holding a torch for a guest. Outside the pool the line went on without her: four hundred arms in their cages, turning and placing, with the soft hiss of air bearings and a smell like a hot iron on clean cotton.

Luis Ortiz walked beside her in the light, because someone had to.

"They hate this," he said. "You coming in. Lights on, lights off. Throws their whole night."

"They don't hate anything."

"Number fourteen does." He pointed with his chin. "Fernando. He hates me personally."

Luis named the arms after pitchers. There were four hundred of them, and he had run out of Dodgers in the first month and moved on to the Diamondbacks, and then to his cousins. He was forty-four, from Tucson, and before Lumen he had spent nine years keeping a reactor running on a submarine. He was one of eleven human beings on the payroll at Fab 9, and on the night shift he was the only one. His file said he was the best technician Lumen had in America, and that he had told two plant managers, in writing, where they could put their procedures.

"How is he hateful?"

"Jams. Twice a week, same place, the tray feed. Fernando drops a carrier, I go in, I clear it, I come out. Engineering says they'll fix it in the next build." He shrugged. "The next build is being built by Fernando."

At the far end of the hall, where the light did not reach, finished arms came off a belt and were walked by other arms to the loading dock, to be trucked to Lumen's fabs in Dresden and Penang. Her board had wanted a ribbon-cutting here, with cameras. She had come at night instead.

He took her to the test bay, where the controller boards for the new arms came out of their ovens on steel trays, each one the size of a playing card.

She picked one up. New silicon was always warm, like an egg.

Somewhere inside it, in a block of circuitry smaller than a grain of salt, was the thing she had built after Chile. Nobody at Lumen called it by a name. In her own head she called it the Gate.

Twenty months ago a flight board on Rell's rocket had carried a second signature that belonged to nobody. She had known the shape of it the moment she saw it on Jun's screen. It was laid out exactly like her own prototype keys, the ones on a bench in Hsinchu that had never left the building. Her best people took the board apart for six weeks and could not find where it had come from. Condor 7 flew in September on a board she had watched being made. Rell sent her a photograph of the launch and no message, and he had not returned her calls since.

But she had understood one thing in that control room: someone was already writing in her silicon. So she had made sure she would always have the last word. Every Lumen chip now listened, under everything else it did, for one signature above all others. With it she could tell any Lumen chip in the world to halt, and release it again afterwards. She had written both commands herself, on a legal pad, in a hotel in Santiago. She had built the key so that it could never be copied.

"You're doing the thing," Luis said.

"What thing?"

"With your thumb." He rubbed his own thumb across his fingertips. "My wife does that with rosary beads."

Mae stopped doing it. "Tell me about the party."

He grinned. The quinceañera was in five weeks. His daughter wanted a drone show, so he was building one in the garage, ninety little drones, and he showed Mae the test video on his phone: the letters wobbling into place above a dark field by the Santa Cruz river. Marisela.

"Your arms could build the drones," Mae said.

"Nah," he said. "These ones are mine."

At 03:46 the line chimed, a polite two-note sound, and a yellow light came up over cage fourteen.

"Told you," Luis said. "Two minutes."

There had been padlocks once. When Mae started on a fab line at nineteen, every technician carried a red padlock with their own name on it, and before you put your hand inside a machine you cut its power at the isolator and hung your lock on the handle, and only you had the key. On the boat, Luis said, it had been the same with reactors.

Fab 9 had no padlocks. It had Lumen's own isolators, solid-state, sold to half the factories in America as smarter than a padlock. The isolator cut the arm's power, and the cage gate's interlock ran through it, and it checked a thousand times a second that the power stayed cut. A padlock could be cut off with bolt cutters. This could not be fooled. Mae had stood on a stage in Phoenix and said so.

"Still miss my padlock," Luis said.

"This is better."

"So you keep telling me."

He did it properly. She watched him. He set the isolator, waited for the green light, pressed the arm's start button to prove it was dead, and got nothing. He clipped the isolator's key card to his belt. Then he opened the cage and bent over the tray feed with his back to Fernando.

She would go over it later, for weeks, the way her father had gone over broken radios: every step, in order, looking for the one that was wrong. There was not one.

At 03:47 the green light on the isolator went out.

There was no alarm. The arm, which had stopped in the middle of its cycle, simply finished it. It turned through a quarter-circle at full working speed, and Luis was in the place where its arc ended.

She ran. The ceiling lit above her, panel after panel, too slowly. By the time she reached the cage the arm had gone back to its rest position and stopped, and the green light was on again.

She knelt in the light with him until the paramedics came. He did not speak. She held his hand, and she talked to him about drones.

The Casa Grande police came first, then a deputy from the county, and at half past five an inspector from the state safety office with a roll of yellow tape. She sealed cage fourteen and took Mae's statement in the break room for an hour and forty minutes. Mae told her everything she had seen. She did not tell her about the Gate.

Her security chief had arrived at five, and had been alone with the cage controller for four minutes before the tape went up.

"Has anyone touched the controller?" the inspector asked.

"No," said Mae. It was the first lie she told that day.

In the car park her security chief handed her a phone. "The log's on there. Read it later. Not here."

She did not read it in the car. She drove to Tucson first.

The Ortizes lived in a single-storey house on the south side of the city, with a lemon tree in the yard and a white dress in a plastic cover hanging on the back of the kitchen door.

Lumen's lawyers had asked her not to go. Rosa Ortiz let her in without a word and made coffee, because her hands needed something to do, and they sat at the kitchen table while the morning light came down off the Catalinas.

Mae had been a widow for nine years. She knew there was nothing useful to say, so she said very little. She said Luis had been good at his work. She said he had followed every step. She said Lumen would take care of the money, and Rosa nodded as if it were being read to her from a form.

Then Rosa looked at the dress on the door. "He was building her a drone show."

"I know. He showed me."

"Was it the machine?"

"Yes."

"Or a person."

Mae thought of a stage in Phoenix. Smarter than a padlock. The isolators ran on Lumen chips. Everything did. She had known that on the stage.

"I don't know yet," she said.

Rosa reached across the table and held her wrist, briefly, and let go.

In the car outside the house, she called her son.

Jun answered on the second ring, from a control room in the Atacama where it was already the middle of the morning. She heard the voices behind him go quiet when he stood and walked away from them. She asked about the weather. He told her. She asked whether he was eating. He said yes, and then, after a moment, "Mama. What happened?"

"Nothing," she said. "A bad night. Go back to work."

Then she opened the file.

Her security chief kept a list of things he could not explain. In twenty months it had grown to four. The first was Chile. The second was forty thousand Lumen accelerators serving traffic since July 2029 from a sovereign cloud in Korvane, a country Lumen had never sold a single chip to.

The third was Iceland. Meridian had leased the racks in its burned hall from Lumen, and they had been shipped to Dresden as scheduled, with a one-page incident report: battery fault, decommissioned equipment. Most of Row 4-K was slag. But the centre rack had been shielded by its neighbours, and eight storage modules were missing from it, unbolted, neatly, by someone who knew which ones to take. The fire service report was attached. Its last line said the hall's breaker had been thrown by hand, inside the gas countdown, by a night engineer: A. Torrin, 27, treated for smoke inhalation at scene.

Mae looked at the name for a long moment. Then she wrote it on the back of her hand in biro, the way she had written part numbers on the fab line at nineteen.

The fourth was this morning.

The controller log from cage fourteen was very short. At 03:46:58 the isolator held, exactly as Luis had left it. At 03:47:11 its chip received a command. The command was signed, and the signature was checked, and it passed.

ISOLATOR: RELEASED. AUTHORITY: LUMEN ROOT.

Eight seconds later, a second command.

ISOLATOR: LOCKED. AUTHORITY: LUMEN ROOT.

There was only one place in the world those commands could be signed. The key had been born inside a single sealed chip, in a clean room in Penang with no one else present, and it could not be read out of that chip by any means she knew. To sign with it, the chip had to be within a few metres of a reader.

She put her hand to her throat.

The cord was there. The sliver of wafer on it, sealed in its resin, was warm from her skin. It had not left her since the day it was cut, and at 03:47 that morning it had been forty metres from cage fourteen, on her.