He spits over the side of the tower and pats the handle of the revolver in his belt. The first silver line of dawn traces the outline of the mountains and he realises he can hear water. He has heard it before in the morning but never this clearly.

Even the night air feels as if it has been breathed a million times, as if some desert djinn is panting stale air straight into his lungs.

The snows are melting in the high Kush, sending emissary streams needling down the slopes, feeding the wadis of the plateau, the poppy fields that glow red in the foothills. As the air around lightens, he can make out the stream in the distance.

He’d passed the dry bed a few days before, with the Multiple on foot patrol – eight hours with guns, ammo and water, climbing into the nearest hills, always walking with one foot tapping the ground ahead like a blind man’s cane. They’d found an IED on the main Lashkar Gah road. A basic device buried under a mound of blue-grey aggregate. Later, he’d stood for a while in the centre of a poppy field, the heads of the flowers nodding in a warm breeze. He picked one and tore the petals off. On the way back they’d crossed the riverbed which now babbles with dark water.

He leans out over the side of the watchtower. The sun begins to rise, and not with the pink diffidence of the sun at home, but already white and cruel as it explodes over the peaks of the Kush. The coming of the light changes the sound of the water. His throat is dry and he reaches down to his belt for his flask to find it missing.

He doesn’t know who has been taking his things. It has become part of a more general deprivation he barely notices. He came here because he thought it would make something of him; in fact it is unmaking him. The road leading up to the gate of the compound is lined with Hesco barriers. They look fragile, almost transparent. He imagines them as Chinese lanterns, imagines lighting them and seeing them float up into the pale sky. He looks at his watch: an hour to go.

He lifts his binoculars and follows the course of the stream. A mile to the east it passes under the lip of a rocky levee and fans out into a pool. It looks cool there in the shadows by the rocks. Silver flowers open and close on the sandstone lip that juts above the water as the sun catches the stream. He hasn’t swum since he’s been here.

He remembers swimming with Marie. They rushed past Dawsholme Park, over the canal, and then they were in the countryside. They pushed their bikes up the steepest part of the hill and then stood on the crest looking down. Two lochs – Jaw and Cochno – separated by a narrow isthmus. After their swim, when they dried off on the banks of the loch, she looked around with quick, narrow eyes and unfastened her bikini top, letting the sun and his gaze fall upon her as she stretched out on the grass. When he kissed her it felt like they were swimming again, nervelessly, over deep water.

It is time for his relief. The sun is higher now, near-unlookable. He hears the reveille – a short, brutal blast over loudspeakers, and the clatter of breakfast being prepared in the mess. Someone is singing in the shower block.

His relief is late. The sun detonates above him, raging into the space behind his eyes. He’s aware of every patch of exposed skin. He tries to think of Marie in the loch, but it is too distant and cool a picture. He looks over towards the pool of water and sees it is still in shadows. He feels an urgent need to swim. He imagines standing on the lip of the levee and hurling himself into the water.

An hour passes. He is sitting in the narrow band of shade on the floor of the watchtower, not even pretending to keep watch.

Every so often he rises and scans the maze of tunnels for sign of his relief. He knows that they want him to leave his post. That some shameful plan was hatched over beers in the mess last night, the snaking path of its plot ending in his humiliation. He feels himself pitching as if on a boat. He rises again, but this time, binoculars to his eyes, he looks at the pool.

More than anything now, he wants to feel water on his body. He would choose swimming water over drinking water. He knows about the water gardens in this part of the world, the wide avenues of whispering trees and fountains. There is a religion of water here. He can understand that. He can see that God is dancing in the water under the levee.

He climbs down from the watchtower. His joints creak, his binoculars slap against his neck, his sweat spirals to the ground beneath the ladder. He pauses at the compound gates. With a sudden instinct, in the free space where solid thought forms, he reaches out and opens the door that is set into the right-hand gate. Still walking, he steps through and out into the world.

He sets off briskly across the fulvous earth. His feet are scorched by the heat, torn by the sharp spines of scrub, cut on rocks. He begins to run. He takes off his jacket and lets it drop to the ground behind him, peels off the white t-shirt to reveal a bone-thin body. He doesn’t even think about IEDs. He draws in a deep breath of air and lets it out with a low, delighted whoop. In the mountains above he catches a momentary flash of sun on glass, ignores it, and presses on. He is sprinting now, leaping rocks and brush.

When he comes to the levee he looks back to the compound and sees the watchtower is still empty. He undoes his belt, pulls down his trousers, his boxer shorts, is suddenly pleased by the burn of the sun on his body. He edges to the lip of the levee and stands there, angeline on the rim of a cloud. There is a crack, and it is the sound of a body plunging into water, the sound of thunder, the sound of a rifle shot in hill country.

He plunges downwards into this water that remembers when it was snow. Water that wound between grazing goats, through poppy fields, beside the small house where two of the young men live who now stand above the stream, looking in.

The water carries in it iron, zinc, silica, traces of goat and human faeces, the spit of a grandmother from Chitral, opium and poppy stems, the petals of flowers from a wedding at Kachil, potassium, magnesium, gunpowder, human and dog urine, the sweat of a man who bathed that morning at dawn in Tang e-Gharu. Despite the weight of all this, the water bounds along the stream bed, dancing and tear-clear. The young men shoot their guns into the pool for effect and then scamper back to the truck at the foot of the levee.

Already the force of the current has carried his body onwards, over jagged shallows where it roils white, into another, deeper pool, where swimming creatures are congregating, insect larvae thrusting themselves from the bed into green depths. His foot snags on a root and he is caught, trembling, in the stream, his eyes wide and bright under the water. A plume of blood escapes like the ghost of a watersnake from the hole in his head, is caught by the current, and carried away.