Thandeka Ruiz-Okamoto did not wear the blue jacket. That was the first thing Zee noticed through the glass: a grey hoodie, a rucksack held on one shoulder like a baby, a woman who had the walk of someone who had quit something an hour ago and was still working out which pocket to put the feeling in.

Seun had retreated to the stairwell with his phone. The lift display had gone dark again, the way a sulking child goes quiet. Zee pulled the door open before the bell could ring.

"I'm not here for the pucks," Thandeka said. "Before you ask. I'm not carrying a single wire."

"Noted."

"I resigned at seven. By email, so nobody could talk me down." She held out a flat, slightly scuffed tablet. "But I took this. Technically it's theft. Technically I'm a thief with a pension plan, so I need somebody to look at it before I start feeling brave."

They went in. Rui had come down to the desk by then, shoes untied, his headphones round his neck, a mug of tea held in both hands as though it were a small animal. He gave Thandeka a nod of grave courtesy. She gave him a nod back. It was the greeting of two people who had both listened to the same terrible audio file.

"The Wharf copy," Thandeka said. She laid the tablet on the desk and woke it. "That's what they call it. The lab is in a converted wharf shed, third floor, no windows, very beautiful. There's a room called the Quiet Room, and in the Quiet Room there's one terminal that does nothing but play your clip."

"How many times?"

"Four hundred and twelve, when I left."

Zee's good hand, the right one, tightened on the edge of the desk. "Each play adds eleven seconds."

"It adds eleven seconds to the room where it's played. I checked the logs. In the Quiet Room it's an empty chair. It's just a chair, a screen, a woman called Odile who sits and takes notes. Every time it plays, it shows the Quiet Room, a bit longer, and nothing happens. Nothing at all." She glanced at Rui. "For four hundred plays. And then last night somebody changed the setting. They set the playback to follow the signal."

"Follow it where?" Rui asked.

"To wherever the clip's other copy is playing. Which is here." She tapped. "They turned the Quiet Room into a window. Here's the last play. I recorded it on my phone. It's thirty seconds of the new footage, not the whole thing. They're getting this, from here, from the ceiling camera, live, with a few seconds' delay."

The screen filled with the lobby. It was the lobby as seen from above, wide and tilted, bright with morning: the desk, the fern, the long tiled floor, the three of them gathered like a conference. In the footage Rui was lifting his tea. Zee was frowning at the screen.

She didn't like how well they had been captured. She didn't like how pleased with it the footage seemed.

"Play it for us," she said. "Properly. Here. In this room."

"That's the idea. If I play it here, it adds eleven to this room. It'll show what's coming." Thandeka licked her lips. "I was hoping it wouldn't show anything. I was hoping it would be the three of you looking at a tablet."

Rui put the tea down. "One variable at a time," he said quietly. "We're changing the room, the device, and the source copy. That's three."

"It's the only way to see what they see," said Zee. "Press it."

Thandeka pressed it.

The tablet gave a small, dry click, like a knuckle, and the footage ran: thirty seconds she recognised, and then a cut so smooth it was almost kind. The lobby gave way to the pavement, shot from some high angle, the camera over the front door. Grey light. The blue van at the kerb. A woman in a grey hoodie came out of the door, rucksack on her shoulder. She looked back once, fiddled with her keys, and stepped off the pavement to cross the road behind the van.

The footage did not warn them. It never did. A white delivery truck came round the corner of Rua das Marés, too fast, with the high, cheerful engine note of a vehicle whose driver was reading something. It took the woman at the hip. It was dreadfully quiet. The picture shook once and went on shaking, and the van's wing mirror folded back like the wing of a bird.

"That's me," Thandeka said.

"That's in four minutes," said Rui, who had counted the time stamp.

"No." Zee was already moving around the desk. "That's in eleven seconds. It runs from now."

"Zee. Wait. What are you doing?"

"What I do." She put her bad hand flat on the tablet.

There was the usual fall. She had stopped trying to describe it to herself: the lobby came loose from its edges, the sound drained to a thin bright whistle, and the floor went from under her without her feet leaving it. A pressure behind the eyes, a taste of burnt sugar. Then the pavement slammed up against her boots and the cold of the morning went through her shirt.

The kerb. The van. The door of Casa Alvorada, closing behind her, and somewhere behind it Rui's voice, small and distorted, saying her name as if from the bottom of a well. She had perhaps five seconds. Thandeka was a pace ahead, stepping off the pavement, keys in hand, a few feet from the corner.

Zee did not shout. Shouting was predictable. She ran, one hard shove, her right shoulder into Thandeka's back, and the two of them went down over the bonnet of the van in a tangle of hoodie and limbs, and the truck went by behind them with the unhurried roar of a train, a hand's breadth from the folded mirror.

It took the mirror off. She heard it go: a bright plastic crack.

Then the whistle stopped, and the sound came back as a sudden flood, and she was lying across a warm bonnet with a stranger's elbow in her ribs, and a man's voice was shouting from the cab of a truck sixty yards down the road, brakes shrieking, and she was perfectly, utterly sure she knew this woman.

She had her face an inch from Zee's. She was breathing hard. She had brown eyes, a split lip, a chip off one front tooth. She said, in a tone of polite concern: "Are you okay, miss?"

"Fine," said Zee. "I'm..."

She stopped.

She could see the word. She could see the shape of it, a long word, with a Z at the front like the blade of a knife. It was her own name. She had said it ten thousand times, signed it on a thousand forms, had it shouted across a crowd. She had it in her mouth. She had it exactly where it should be, and it would not come.

"I'm," she said again. "I'm..."

Thandeka's face changed. "Oh, no. No, no. Hey. Hey, look at me. Zee. Zee. Come on."

"Zee," said Zee. It was a sound with no weight. "Is that me?"

Then Rui was there, kneeling on the wet tarmac, his hands on her face, so careful. He had run out without his shoes, and his socks were soaked. He said, "Hello. Hello, listen to me. You're Zainab. Zainab Oyelaran-Pereira. Everybody calls you Zee. You work nights. You count things. You hate custard tarts. You're thirty-three."

She watched his lips. She heard each word and each word was true, and none of them attached. They slid past her like cars. She was standing, on a pavement, looking at a stranger who loved her enough to be lying to himself about his socks, and she understood, with a calm so deep it was almost restful, that she did not know who he was talking about.

"Okay," Rui said, to himself. "Okay. All right. Don't panic. Think of it like a dropped sample. The audio's there, it's just not being read. We need a reference. Give me a reference."

He took her good hand, the right, and put it against the left side of his own head, against the ear that did not work. It was warm. There was a faint crust of dried sweat at the temple. Under her fingers there was a pulse.

"That's me," he said. "That's Rui. I can't hear you on this side, and you always walk to this side so I can't hear you either, and you think I haven't noticed. You said it's because you like to be quiet with me. Do you remember?"

She did not remember.

But her hand knew his pulse. She felt, in some floor of herself, the thing she did every time she came near him: the tilt, the lean, the tiny adjustment of her body so that her mouth fell toward the dead ear and her good side stayed clear, as if to say, I won't make you work.

"Rui," she said. It came out of her like a coin out of a slot. "You smell like tape glue."

He made a noise that was half laugh and half something else, and put his forehead against hers.

The name came back after that, in pieces. The z, the a, the i, the n, like a bad connection finding its bars. Zainab. Zainab Oyelaran-Pereira. She stood in the thin cold light on the pavement, shaking, with Thandeka still holding her sleeve and the truck driver running toward them with his hands over his head, and she knew every word of it. She did not feel like the same woman who had owned it.

She checked her watch. Three minutes. She had been nobody for three minutes.

"I'm fine," she said. "I'm okay. Don't make a thing."

"We are going to make a thing," said Rui.

It took twenty minutes to deal with the truck driver, who was young and appalled and kept saying he'd just looked down for a second, which Zee permitted him without comment, because she knew that sentence like her own pulse. Thandeka gave her name to a municipal policeman and refused an ambulance. The van's mirror lay in the gutter in two pieces. Seun stood in the lobby doorway holding the door open with one foot, his phone dangling from his hand, his face the colour of paper.

Back inside, the tablet had gone dark. Zee stood at the desk and looked at the pale print on the floor beside her chair, and she did not need to count. She had learned to know the number before she looked.

The print had moved. It was no longer beside the desk. It was in front of it, on the near side, the customer's side, a little closer to the lift than before. The newest was wet.

"Zee," Rui said quietly. He had followed her gaze. "Is that..."

"Six uses," she said. "Six places closer. There are only so many places."

Thandeka had picked the tablet up again. She had gone very still, with her split lip and her chipped tooth and her rucksack hanging by one strap. She was reading something on the lock screen, something that had come in while the footage played.

She turned it around.

It was a message from a number she had saved as Odile Q. Room. It said: Thank you for confirming the Casa Alvorada loop. Ms Vorster-Anand will be bringing her visit forward to this afternoon. Please tell Ms Oyelaran-Pereira that we are so looking forward to meeting her.

Below it, a small grey line of metadata. Delivered 08:41. Read 08:41.

Read, Zee thought, by someone who had been watching the whole time.