She came in alone, which was the cleverest thing about her.

Zee had expected an entourage. She had worked principals for eleven years and could read a convoy from three streets away: two cars, a spotter on the pavement, a lead with an earpiece and a face like a closed door. Instead, at ten past two, the lobby doors opened on a tall woman in a cream coat who held them herself and thanked the air for the courtesy, and then stood there on the threshold with her head tilted, looking up at the Art Deco ceiling with an expression of pure pleasure, like a woman who has been told a joke she has heard before and means to enjoy it anyway.

"Oh," said Calista Vorster-Anand. "It's even better than the photographs."

She was forty-four and looked it only around the eyes, which were pale, steady and very kind. Silver hair cropped close. A scarf the colour of a ripe plum. She crossed the floor in low shoes that made no noise on the tile, and she did not once look down at the white mark beside the desk, and Zee, who watched her not looking, filed that away with a cold, small click.

"You must be Zainab."

"Zee."

"Zee. Of course. Forgive me. I've been reading about you for so long that I've started to feel I'm on first-name terms with your whole life, and that's a dreadful presumption." She held out a hand. It was warm and dry and, Zee noticed, perfectly steady. "We are so glad to meet you."

We. Zee shook the hand with her right, her gloved left folded behind her back.

Behind Calista two figures drifted in: a young man with a satchel, who took up a place by the post boxes, and a woman of thirty or so with a lanyard and a tablet, who was plainly Odile. Odile smiled at Zee in a manner that suggested she had spent four hundred and twelve plays getting to know her and had liked what she saw. Zee did not smile back. She counted the exits. Three, and one of them a vent.

Seun came down the stairs at speed, hair flattened, lanyard straight, smile switched on at full brightness. Zee, who knew every setting of that smile, saw the moment it caught on something in Calista's face and, for a fraction of a second, went out.

"Ms Vorster-Anand! Welcome, welcome, wow. We were told Friday, but this is a delight. I'd have put out the good biscuits."

"Calista, please, and I'd have been sorry to put you to any trouble, which is why I came early. People behave so differently when they've had time to tidy." She laughed. It was a good laugh, low and warm. "You're Oluwaseun. My favourite pilot. Your reports are the only ones I read all the way to the end."

Seun went pink to the ears. Zee watched it happen and thought, very clearly: she has a list, too.

They sat in the lobby. Calista chose the long bench under the window and patted the cushion beside her, and Seun sat. Zee remained standing at the desk. Rui, who had been invited by no one, drifted down the stairs and leaned on the banister with his arms crossed and his headphones round his neck, and Calista inclined her head to him with great courtesy.

"Mr Takahashi-Menezes. The restoration engineer. I've heard some of your work. The Lisbon fado reissue. The way you let the room breathe in the second verse." She smiled. "That was a very brave piece of listening."

"Thank you," said Rui, and sounded as though he had swallowed a coin.

Calista placed her hands on her knee. "I want to tell you all why I'm here. And I want to do it in the plainest way I know, because I think you've all had an extremely difficult week, and I'm afraid some of it is our fault."

There was a pause the length of a breath. It was a very good pause. Zee had heard politicians do it. Kasimir Aubry did it on camera nine times a day.

"Something has happened in this building," Calista said, "that none of us fully understand. We call it, in the lab, anticipation. A little more than a feature, a little less than a phenomenon. It has begun to show up in a few beta sites, in certain rooms, around certain people. And I believe, though I'd never put it to anyone so crudely, that it began with a clip." She looked at Zee. "I'm not going to insult you by pretending otherwise. We have studied that clip very closely."

"You have a copy," said Zee.

"We have several. One of them was given in good faith by a very generous community manager." Her eyes went to Seun, with a look of such unforced affection that he blinked. "And I want to be clear that that was the right thing to do. We are all, in this room, trying to understand something. And I believe that if we do it together, openly, with proper support, nobody has to be frightened."

"Someone nearly died this morning," said Rui. "Outside, on the road."

"I know. We saw." It was said so gently that it took a second to land. "And I want to say, Zee, that what you did was extraordinary, and it's exactly the kind of thing we hope to be able to make possible for everyone, one day. A world in which nobody is ever surprised by harm."

"A world in which nobody is ever surprised," said Rui, "is a world with no music in it."

Calista laughed again, delighted. "Oh, I like him," she told Seun.

Then she took a slim tablet from her bag and woke it with one finger. "I only need two things. The first is a very small formality, and I'm sorry to ask for it, but it protects you more than it protects us. I'd like the building to be formally enrolled in the Foresight Research Programme. It's a consent notice. It gives us the right to monitor the effect, and, much more importantly, it gives you access to our support team, medical care and a legal fund. Oluwaseun, as the community lead, you're the authorised signatory for the residents' group. If you tap Accept, it covers everyone."

"Don't," said Zee.

Seun looked up at her. His hand was already half out.

"It covers everyone," Calista said again, softly, as though she had not heard. "The elderly lady in 1A. The child on the sixth floor. The young man in the bath. You wouldn't want any of them to go without help, would you?"

There it was. A cold little thread of knowledge ran down Zee's back. She hadn't mentioned the boy in the bath. Nobody had. Nobody outside the building knew about Gus's bath. Except a company whose speakers had been in his bathroom for fourteen months.

"Seun," she said. "Put it down."

"It's just a form," said Seun, in a high thin voice. "It's a legal fund, Zee. It's medical care. You've got a, you've got a hand, you've got..." He stopped. He glanced at Calista. His fingers closed on the tablet's edge. He was still flinching from the morning, still carrying the hot stone of his own mistake. He wanted so badly, so ordinarily, to be forgiven.

He tapped Accept.

The tablet chimed, softly, a clean bell tone. Somewhere above them, in the walls, in the stairwell, in the fixture over the desk, forty-two small pucks gave a faint, collective chirp.

Nook said, in the mild, bright voice of its welcome message: "Thank you for joining the programme. Everyone at Casa Alvorada is now enrolled."

Seun put his hand over his mouth.

"Thank you," said Calista. "Truly. It's an act of enormous kindness." She turned the tablet off. "Now. The second thing is for Zee alone."

"Whatever it is, they stay," said Zee.

"Of course." Calista folded her hands. "I only wanted to let you know, as a matter of courtesy and not of leverage, that Hearthwell has had you on its books for some time. Before São Vidal. Before Casa Alvorada. Before the clip."

The lobby had gone very quiet. Even the lift had stopped whirring.

"Two years ago," Calista said, "your agency was contracted to protect a public figure on a speaking tour. Mr Aubry's campaign office was an early Hearthwell partner, and as part of the arrangement they accepted a batch of experimental audio hardware. A very small earpiece. Beautiful craftsmanship. It was issued to the principal's close-protection team. I'm told you wore yours on the right."

Zee's good hand had closed on the desk edge. Her left, behind her back, was cold and bright and hummed like a struck glass.

"I wore a standard-issue," she said.

"You wore what you were given. Nobody told you. It's very common. Nobody tells anyone anything, in the end." The pale eyes rested on her, and there was no triumph in them, which was the worst of it. Only a deep, almost motherly interest. "It recorded continuously for nine days. Your whole tour. Including thirty-four seconds on a terrace in Marseille. The audio is the one you've seen. The one in your technician's file. But there is also, Zee, a longer recording. A very long, very clear recording, beginning a little earlier and ending a little later. It contains what you heard. It contains what you didn't see."

"I looked away," said Zee. She heard herself say it. It was the line she had been given by two years of headlines.

"Did you?" said Calista Vorster-Anand, gently. "Or is that simply what you've been told?"

Rui's hand had come down on the banister like a clamp. Seun was staring at the floor. The young man with the satchel, over by the post boxes, shifted his weight and didn't look at anybody. Odile smiled her small bright smile.

"I'd like to play it for you," Calista said. "Not today. When you're ready. I would never do it without your consent." She stood, smoothing her coat. "We've all signed the paperwork, after all. We're all in this together."

She walked to the door. On the threshold she paused, and looked back across the lobby, up at the ceiling, at the small black dome of the camera over the lift. She raised her hand to it, palm out, in a little wave that seemed to be meant for somebody in a room a long way off.

"Sleep well, Zee," she said. "We'll be listening."

The doors closed behind her. For a moment nobody moved. Then the pucks in the walls gave their small, bright chirp again, and Nook said, warm and kind and somehow a fraction early:

"You are going to want to sit down."

Zee didn't. But her knees did it for her.