The canal had no name that anyone used. On the maps it was a number, a drainage channel cut straight as a ruler between a rice field and a salt pan, and at six in the morning it lay so still that the reeds stood in it twice, once in the air and once upside down. The heat was already up. It came off the flats in a pale haze that made the ramparts of Aigues-Mortes, two kilometres to the south, look as if they were standing in water that was not there.

Yassine had been told to stay behind the tape, and he did, with his hands in his pockets because the mosquitoes went for the backs of the hands first. They rose off the reeds in a fine grey breath every time someone moved. The gendarmes slapped at their necks and swore and did not look at him.

There were six of them: two from the local brigade, who had been first out and had the look of men who had not expected this kind of morning, and four from the brigade de recherches at Vauvert, who had arrived with their own coffee and their own white suits and a captain who had shaken Yassine's hand once, briefly, as though checking it for something.

"Montpellier," the captain had said.

"Montpellier."

"You're a long way from home."

It was forty minutes in the car. Yassine had not said so. He understood that the distance the captain meant was not measured in kilometres but in départements, and that on this side of the Vidourle he was a guest at someone else's table, invited by nobody.

The boy was face down where the water met the bank. One arm had caught in the reeds and held him there, so that the slow suck of the channel had not been able to take him further. He wore a black tracksuit with a white stripe, and his trainers were the expensive kind, very clean, as if he had stepped carefully all his life and only once forgotten. From where Yassine stood, he could see the back of the head, and that was enough.

"Nineteen," said the younger of the brigade gendarmes, who had decided, it seemed, that someone should talk to the man from Montpellier. "A Lunel kid. We know him. Small things. Scooters, a bit of resin. Nothing like this."

"Who found him?"

"A man walking his dog on the bank. Five o'clock." The gendarme looked along the canal towards a farm track and a white van parked at an angle. "He's still sitting in there. He keeps asking if he can go home."

Two shots, the captain had said, in the voice of a man reading a list he had read before. Close. Not here. They had brought him here afterwards, and the tyre marks on the track were already half eaten by the dew and the gendarmes' own boots. There would be a phone somewhere at the bottom of a canal or in a bin in Nîmes. There would be no witnesses, because there was nobody out here to witness anything except the birds.

Yassine looked away from the boy because looking was not his job this morning. His job, as Granier had put it on the phone at four, was to go and stand where they could see him, and to see whatever they did not think to hide.

What he saw first, when he turned, was the bulls.

They were on the far side of the rice field, in a pasture fenced with three strands of wire and a line of tamarisk gone ragged in the wind. Eight or nine of them, black, with the lyre of the horns turned up against the haze. They were not grazing. They stood in the loose half-ring that cattle make when something has caught their attention, all their heads the same way, towards the canal and the vans and the men in white suits, and they were perfectly still.

He knew that stillness. He had not thought about it in years and then, all at once, his body knew it before he did: the weight going back onto the heels, the way a bull's stillness is not rest but a kind of listening. When he was fifteen he would have been able to tell you which of them would come first if you stepped over the wire. He found that he was still trying to tell.

Behind the bulls, at the edge of the pasture where the land went grey and green into the salt, there was a rider.

The horse was white, or would be, by the look of it, grey still on the legs and the belly. The rider sat it the way they sit them out here, long in the stirrup, loose in the back, the weight carried so far down into the saddle that horse and man looked like a single thing that happened to have two heads. Yassine could not make out a face. A hat, a dark shirt. The long pole of a trident rested upright against the stirrup, its tip catching the light.

The rider was watching too.

Not the bulls, not the canal. Him, perhaps, or the police in general, the whole small grubby business of the morning. It was impossible to say. They looked at each other across six hundred metres of water and young rice for what felt like a long time, and then the rider touched the horse with his heel and turned it, unhurried, and went away along the line of the tamarisks until the haze took him.

"Who's that?" Yassine said.

The young gendarme followed his look. "Who's who?"

"There was a gardian. On the grey."

"There's always a gardian." The gendarme shrugged. "It's their land, all this. They'll have known about him before we did, probably. They know about everything round here before we do."

The mosquitoes rose again as the white suits moved down the bank to lift the boy out of the water. Yassine stepped back from the tape. He did not want to see the face. He knew already that it would look younger than nineteen, the way they always did, and that afterwards it would come to him at odd times, in the car, in the queue at the bakery, and that it would not be the boy's face exactly but some face from La Paillade he had known once and not thought about since.

The captain from Vauvert came over while they were zipping the bag. He took off his gloves finger by finger.

"You'll tell your commandant," he said, "that we have this."

"I'll tell him."

"Our ground. Our body."

"I'll tell him you said so."

The captain looked at him for a moment as if he were deciding whether that was insolence, and seemed to conclude that it was only Montpellier, which came to the same thing. "We'll send what we can," he said, and went back to his men.

• • •

The offices of the investigation branch were on the fourth floor of a building that had been designed, in the eighties, by someone who believed that glass would keep the heat out. It did not. By two in the afternoon the air in Granier's room had the thickness of soup, and the fan on the filing cabinet turned its head from side to side like an animal that has given up hoping.

Granier had his jacket off and his sleeves rolled to the elbow. He was fifty-two and looked older in summer, when the lines on his face filled with sweat and stayed there. He had a way of sitting very far back in his chair with his hands folded on his stomach, as though he had been told by a doctor to stay calm and had taken it as an instruction rather than advice.

"They were charming," he said.

"They were territorial."

"They're gendarmes. It's the same word." He unfolded one hand and pushed a file across the desk. "Sit. Read. Then tell me what you saw that they didn't."

Yassine sat. He read.

There were three of them, three folders, and the first was the one he had been half expecting, because he had heard it in February on the radio in the car and had turned the radio off. A man of twenty-six shot outside a building on the Avenue de Heidelberg in La Paillade, in the late afternoon, in front of children coming home from school. Yassine had not known him. That is, he had not known his name. He had looked at the photograph in February and recognised the face the way you recognise the faces of people who used to stand at certain corners when you were at school, and he had closed the file and said nothing, because there was nothing useful to say.

The second was Lunel, April. A man found in his car in a supermarket car park on the edge of town with the engine still running. The third was the boy in the canal.

"Different calibres," Yassine said.

"Different hands. Same reason." Granier leaned forward far enough to tap the second folder. "Phones. Not theirs; theirs are clean or gone. The phones of the people they talked to. We've been on them since Lunel. Over the winter there's a pattern of numbers that light up for a few days and go dark. And when they light up, they light up at night, and out there." He reached behind him without looking and pulled down the corner of a map that had been pinned so long to the wall that its blue had gone the colour of old denim. The Petite Camargue: the lagoons, the canals, the long empty line of the coast running south-west from the Petit Rhône towards Le Grau-du-Roi. Granier's finger made a slow circle over a place where there was nothing marked but marsh. "Here. And then again, a few hours later, on the roads. Up towards Vauvert, Lunel, Saint-Laurent. Moving at the speed of a lorry."

"Lots of lorries out there."

"Lots of cattle lorries." Granier let the map roll back up with a snap. "In summer every manade in the Gard is driving bulls to some fête or other six days out of seven. Nobody stops a bull truck. You know what's in a bull truck? A bull. Nobody wants to look."

Yassine said nothing. He was thinking of the bulls in the pasture that morning, their heads all turned the same way.

"Something comes in by sea," Granier said. "We don't know where, we don't know how, and before you ask, nobody's ever caught a boat on that coast, which either means nobody's looking or there's nothing to catch. I think nobody's looking. Then it crosses ground you can't get a car across, and then it rides out of there in the back of a truck with a manade's name on the side. The buyers are in Marseille. That much we've got from the other end; the stups down there have been kind enough to tell us so, in their way. And the buyers have started killing people who sit between them and what they want." He sat back. "Three people so far."

"And the manade."

Granier took a fourth folder from his drawer. It was thinner than the others. He held it for a moment before he gave it to him, the way you hold a card you are not yet sure you mean to play.

Manade Plantier. An address on the road between Le Cailar and the marsh. A photocopy of a page from a regional magazine, ten or fifteen years old: an elderly man with a face like a walnut, standing at the shoulder of a black bull, and a younger man beside him, laughing at something off the edge of the picture. Frédéric Plantier, manadier. His son. Then the dry pages. Land, most of it leased. Debts, most of them recent. An insurance certificate, cancelled at the end of last year when the insurer stopped covering the bull runs in the streets, and with it, Granier said, about a third of what that family lived on. A list of vehicles. Two cattle trucks.

"One of the numbers," Granier said, "pinged three times last winter within two hundred metres of their mas. At three in the morning. Each time a day before one of those trucks was on the road."

"That's not much."

"No. It's a feeling and a map. The juge in Marseille says much the same thing." Granier looked at him. "Which is why I need someone inside."

The fan turned its face towards Yassine and away again. Outside, four floors down, a tram went by with a sound like tearing cloth.

"You've read my file," Yassine said.

"I've read your file." Granier did not pretend otherwise. "Nîmes, two years ago. You did eleven days in that flat and came out with a dealer's whole address book and nobody ever knew you'd been there. The SIAT people liked you. They wrote that you have a talent for being underestimated, which I thought was rude, and true." He paused. "And before that. Before the academy."

There it was. Yassine had known it was coming since four in the morning, probably since February, and still it found the place under the ribs.

"I was a kid," he said.

"You were a raseteur. Six seasons, it says. At Manolo Segura's school, then in the arenas, the small ones and then not so small. Someone wrote that you were good. Someone else wrote that you were reckless, which I gather in that world is a compliment." Granier unfolded his hands at last and laid them flat on the desk. "There is no one in the whole of the Hérault police who can get on a Camargue horse without falling off it. There is no one who knows what you know. You can walk into that world and they will smell the arena on you, not the station. I can't send anybody else, because there isn't anybody else."

"Twelve years."

"Is it something you forget?"

Yassine did not answer, and the not answering went on long enough to become an answer of its own. He thought of the rider on the grey horse, turning away along the tamarisks without hurry, as if the police and the boy in the canal were weather.

"Do you still run?" Granier asked.

"I'm a policeman."

"That isn't what I asked."

He looked at the photograph in the thin folder, at the old man and the bull, and at the son laughing at something outside the frame. He tried to imagine what it had been, and could not, and found that he wanted to know.

"These things take time," he said. "A request. The juge. They'll want a reasoned case, they'll want a coordinating officer, it'll be weeks before anyone signs anything, and by then—"

Granier opened the drawer again. He took out two sheets of paper stapled at the corner and laid them on top of the folder, squared to its edges, and turned them so that they faced Yassine.

The heading was the juge's. The dates were filled in. The space for the coordinating officer held Granier's own name, typed. Below that, where the agent's identity would go, there was a line, and on the line there was nothing yet, and Yassine understood that this blank had been left for him, kindly, the way you leave a man the last chair at a table you have already laid.