The Au Pair

Chapter One: The Fourth Floor

The cold had come early to Lyon that November, and by eight in the evening the Presqu'île smelled of wet stone and diesel.

Detective Pascal Aubert took the stairs because the lift in the building on rue Auguste-Comte was the size of a coffin and he did not trust it. Four flights of worn limestone, a wrought-iron banister polished by two centuries of hands, a stairwell light on a timer that clicked off twice before he reached the top.

On the third-floor landing he found the shoe.

It was small, red, a child's canvas trainer with a velcro strap, lying on its side against the skirting board as if it had been dropped by someone in a hurry. He crouched, did not touch it, and looked up the last flight. A woman was leaning over the railing, her face white in the stairwell light.

"Up here," she said. "Please. Quickly."

The door of apartment 4B stood open. A man in a grey cardigan hovered in the hallway with a bunch of keys in his fist — the building's caretaker, Aubert would learn, a Monsieur Bouchard who had let the neighbour in with his master key and now looked like he wished he hadn't.

The apartment was warm and quiet and smelled faintly of vanilla, the way homes with small children often do. A row of coats hung by the door. A pair of ballet slippers sat neatly in a basket. Everything in the place had the tidiness of a photograph.

Aubert followed the woman down the corridor to the kitchen, and there, on the pale oak floor between the island and the fridge, lay a little boy.

He was perhaps three years old, in pyjamas printed with rockets. One arm was flung above his head. His skin had the waxy sheen of a candle, and his lips were the colour of a bruise. A tipped plastic beaker lay near his hand, a thin puddle of milk drying at the edges.

"His name is Hugo," the woman said. She was already on her knees beside him. She was in her seventies, silver hair cut short, wearing house slippers. "Hugo Chartier. I'm Madeleine Roux, I live across the landing. I was a nurse for thirty-one years. He's breathing but it's shallow. His pulse is slow. Somebody has given this child something."

Aubert put two fingers to the boy's throat and felt the flutter under the skin, faint and unhurried, a moth against a window.

"SAMU?"

"Called. Six minutes ago."

"Anyone else in the apartment?"

"I don't know. I heard him crying through the wall. It went on and on and then it stopped, and it was the stopping that frightened me." Her hands were steady on the child even while her voice shook. "Nobody answered the door. I fetched Monsieur Bouchard."

Aubert stood. He was forty-four years old, and he had been a police officer for twenty of them, and he had a daughter of six who at that moment was at his mother's flat in Villeurbanne eating pasta and refusing to eat the courgettes in it. He kept his voice level.

"Stay with him."

He went through the apartment the way he had been trained to, room by room, calling out. Living room: two sofas, a wall of art books, a large abstract canvas in ochre and grey lit by a picture light. Master bedroom: bed made with hospital corners, a woman's silk robe folded over a chair. A boy's room, empty, the duvet turned back. A girl's room, pale pink, a shelf of picture books with their spines aligned like soldiers.

At the end of the corridor, off the kitchen, a narrow door stood ajar. The maid's room. Aubert pushed it open with the back of his hand.

A single bed, stripped to the mattress. An empty wardrobe with eight wooden hangers, evenly spaced. A desk with nothing on it at all. The window was shut and the radiator was off, and the room had the smell of a place that had been recently and thoroughly cleaned. Bleach, faintly. He touched the desktop with a gloved finger. It squeaked.

He was still standing there when he heard the sound.

It was not a cry. It was smaller than that — a rustle, a shifting of fabric, the sort of noise a cat makes settling. It came from the entrance hall.

Aubert walked back up the corridor. The coats hung in their row: a woman's camel wool, a man's navy overcoat, two child-sized anoraks. Behind them was a closet door, flush with the panelling, with a small brass key in the lock. The key was turned.

"Hello?" he said.

Silence. Then, again, the rustle.

He turned the key and opened the door.

A girl sat on the closet floor with her back against the rear wall and her knees drawn up under her chin, in among the boots and the folded shopping bags. She was six years old, in a nightgown printed with strawberries, her dark hair still damp at the ends from a bath. She had one shoe on. The other foot was bare.

She was not crying. She was not doing anything at all. She looked at Aubert with a calm so complete that it stopped him in his tracks, and then she looked past him, down the corridor, towards the kitchen.

"Hello," Aubert said. He went down on his heels so that his eyes were level with hers. "My name is Pascal. I'm a policeman. You're safe now. Can you tell me your name?"

The girl said nothing.

"Are you Celine?"

Nothing.

Below them, four floors down, the street door banged and boots began to come up the stairs two at a time, and the stairwell filled with the crackle of radios. The girl did not flinch at any of it. She watched Aubert's face the way you watch weather through a window.

"Celine," he said gently, "is anybody else in the house?"

She blinked once. Then she turned her head and looked, deliberately, at the empty doorway at the end of the corridor — the little room off the kitchen, with its eight hangers and its bleached desk — and she said nothing at all.

The paramedics filled the kitchen. They intubated Hugo Chartier on the floor beside the fridge and carried him down in a red blanket, and Madeleine Roux went down after them with her cardigan buttoned crooked, telling them in a firm clear voice about pulse rates and pupil size.

Aubert stayed. He stood in the hallway with the closet door open behind him and made the calls.

The mother, Isabelle Chartier, was in Paris at the opening of an exhibition, her phone going to voicemail in a French so poised it sounded like an advertisement. The father, Thierry Chartier, was somewhere over Germany or stuck on the ground in Frankfurt; the airline confirmed his flight had been delayed three hours by weather.

And the au pair — the woman the caretaker described as the one who really ran the place, the polite one, the one who always said good evening and held the door — was not there.

"Camille," Monsieur Bouchard said. He kept turning his keys over in his hands. "Camille Brunet. She's been here since the summer. Lovely with the children. Very correct."

"When did you last see her?"

"Around six? She was carrying a laundry bag down to the cellar. She said good evening." He hesitated. "She used the service stairs. She often does. She says the lift wakes the boy."

Aubert wrote it down. Then he went back to the third-floor landing, where a young officer was already photographing the little red shoe against the skirting board, the flash bouncing off the polished stone.

He thought about a child carried through a stairwell in the dark. He thought about eight hangers spaced like teeth in an empty wardrobe, and a desk wiped so clean it squeaked, and a six-year-old girl sitting silently in a coat closet with the key turned on the outside.

The timer light clicked off. In the darkness, Aubert stood very still.

Whoever Camille Brunet was, she had not run. She had left — carefully, in order, at a time of her choosing, by a door she had known about long before tonight.

He would spend the following weeks learning how long.