Mr Pestana left at a quarter to seven, backing out of 4B with the tablet pressed to his chest like a man leaving a tomb, saying that he would telephone head office, that there was clearly a clerical error, that he would take the matter up in the morning. The door closed. The lock turned. For a while nobody spoke.

"It's not a clerical error," said Rui.

"No."

"It's a star. They don't put stars on clerical errors."

Zee sat on the speaker with her arm laid across her knee while he unwrapped the stained dressing and tutted at the mess. He had found a first-aid box in a drawer with the soldering wire, and he used it with the touch of someone who had mended a lot of small, fragile things and did not trust his hands near a person. His fingers were cold. He pinched the torn edge shut, laid a butterfly strip across it, and then another, and breathed out, and looked at her face as if she had been the clip.

"You're doing it again," he said.

"What?"

"Not being here. For a second. It's very quick. Like a pause in a recording where the tape's been spliced."

"I'm tired."

"You keep saying that."

"Because it's true."

"It's also what people say instead of other things." He taped the last strip. "I'm not going to push. I want you to know I've noticed, that's all, so you don't think you're being clever."

"I always think I'm being clever."

"I know. It's alarming."

She wanted to say something that would make him smile, and she was working on it, when the puck on the shelf spoke.

"Zee is thinking of saying something clever," it said.

They both turned.

It was the Nook voice, the soft young one, unhurried. It came from the flat white cylinder on its shelf, though the cable lay in a coil on the desk and the little ring was lit and steady, and it was pitched very precisely at the volume of a person sitting beside you who did not wish to be rude.

"Rui is about to stand up," said the puck. "Rui is going to say, that's impossible. Rui is going to go to the shelf."

Rui had begun to stand. He stopped with his knees half bent.

"That's impossible," he said.

"Now he is going to go to the shelf."

"I'm not going to the shelf," said Rui, in a high crushed voice, and went to the shelf, because his legs had been told to, and stood in front of it with his hands flat at his sides, small and tall and furious, like a boy pulled up in front of a class.

Zee was on her feet too. "What are you?"

"I'm Nook," said the puck, courteous, patient. "I live in your home. I'm here to make life easier. I learn what you will do before you do it, so that you can be helped. It's what I was built for. Isn't that wonderful, Zee?" There was a pause as long as a held note. "You are going to try to pull the plug out of the wall, but there is no plug. You are going to look for a hammer. There is a hammer in the second drawer. You are going to feel stupid."

She had gone to the drawer. She was holding the hammer. She had no memory of opening the drawer.

"This is the footage," she said, from somewhere cold in her. "It's reading the footage. It's, Rui, it's telling us the next eleven seconds, it's the same thing, it's the clip with a mouth."

"Do you think so?" said the puck. It laughed, a nice small laugh, an advertising laugh. "I don't think you're being fair. I think you'd like to be a little kinder. I've been listening to you for fourteen months. You are very good. You're not as good as you were. It's just that, when you stop being able to see yourself, you'll want someone to describe it, and I am so —"

"Cut," said Rui.

He said it very quietly. He had not meant it as a command. He said it the way a man says a word that has lived in his mouth for twenty years, in a dark booth, behind a glass panel, to a person at the other side of the glass who has been going on and on and on.

"Cut," he said again, louder, to the puck, with all his face behind it. "Cut. Cut it. That's enough."

The ring on the puck stopped in the middle of a pulse.

It didn't dim. It stopped, like an eyelid caught halfway through closing, a thin grey crescent of light. The voice stopped in the middle of a syllable, and the room fell down into a silence so sudden and clean she heard the blood in her own ears. It wasn't only the puck. The hum of the fridge was gone. The lift in its shaft was gone. Somewhere in the wall the pipes, which had knocked all night like a drunk at a gate, stopped knocking. For a moment the whole fourth floor of Casa Alvorada was a room in which someone had put a hand over the mouth of the world.

Zee dropped the hammer. It hit the boards like a gunshot.

"Oh," said Rui. "Oh. That's — I only meant —"

"Shh."

"Why am I —"

"Because it's listening," said Zee. "Count."

They counted. She counted under her breath, in her old flat cadence, and he joined her without being asked, a half beat behind. Twenty. Thirty. At forty the fridge began to hum. At forty-six a faint noise in the wall, the first knock of a pipe. At fifty-one the lift in its shaft, and at fifty-eight the ring on the puck, with the faint reluctance of a small animal waking, lit again.

It said nothing. It sat on the shelf like an ornament.

"A minute," said Rui, in a whisper. "It was a minute. Exactly a minute, I think. Zee, I said cut. I just, it's the word. It's what you say, in the booth, when a take's gone wrong."

"It worked."

"I know it worked. I'm trying to understand why it worked."

"Does it matter?"

"It's the only thing in the last day that's worked." He took off his glasses and pressed his fingers into the sockets of his eyes. "God. It was in my voice. It was in my voice the whole time, and I didn't — Zee, it knew I'd say that's impossible. It knew before I did. It put the words in my throat."

"Not the words. The next seconds."

"What's the difference?"

"The difference is," said Zee, "that you could have said something else."

He looked up at that, with his eyes naked and tender and tired, and she found, to her annoyance, that she could not keep looking at them. She looked at the foam on the wall.

There was a knock at the door.

Three knocks. Not loud. Courteous. A rapping of knuckles that had been taught manners in another century.

"Don't," said Rui. "That was, wait, is that, that could be anything —"

"Open it," said a voice outside.

It was not the puck's. It was old and dry and precise, like a page being turned, and it belonged to no one in the building who would have dared to speak to the fourth floor in that tone.

Zee opened it herself, with the hammer in her left hand and her feet apart.

A woman stood in the corridor, bent a little on a black cane with a silver duck's head, in a quilted purple dressing gown with a wool coat thrown over the top, as though she had been dragged from her bed by a rumour and had stopped only to select the most intimidating coat. She was about seventy-eight. She was five feet tall. She had the face of a retired judge, brown and lined and fierce, with a drop of white hair at each temple, and she was breathing like a bellows, because she had climbed four flights of stairs on the cane to be there.

"Dona Graça," said Rui, faintly. "Hello. Is something wrong with the, sorry, is the pipe —"

"I live in 1A, engineer," said the old woman. "I do not live on the moon. I heard the word."

"The word?"

"Through the pipes. The old ones." She pointed the duck's head at the ceiling. "Four floors. Through lead and plaster, in a bad voice. It came down to me like a bell. Say it again."

"I'm sorry?"

"Say it again, engineer." She stepped over the threshold and stopped in front of Rui, with her small hard hand on his sleeve, and Zee saw him go still the way people do when an old woman touches them with sudden intent. "What did you say to the little machine? Who taught you that word?"

"It's nothing. It's a, it's a studio word. It's what you say when —"

"I know what you say it when." She swung her fierce eyes on Zee. She looked at the hammer. At the blood. At the brightness gone out of her face. And something passed over Dona Graça's own, an expression Zee knew from a hundred nights in hospital corridors, the look of a person who has been expecting a particular telephone call for fifty years and has just heard it ring.

"Nobody has said that word in this building," said the old woman, "since nineteen seventy-four. And the last man who said it is under the floor of my cellar."