The year Bojan turned 10, his father was assigned a sentry mastiff called Kaiser, and when his father came back from the front that summer, he brought the dog to live with them.

Bojan had never had a dog. He had spent the duration of his father's military service living with the housekeeper on the northern outskirts of the city, on a shady linden-lined avenue in a house that had belonged to his family for three generations. The housekeeper, Mrs Senka, was a tired woman with dry yellow hair resembling frayed rope, and she kept mostly to herself, except on Sundays, when she prepared a feast for the women of her congregation. Something about Bojan's excitement concerning the dog's arrival had struck a chord with her, and she had taken him to study the breed catalogue at the library, and to the butcher, so that Bojan himself could pick out the bones he would give the dog.

The mastiff came in a crate with bars on the front. Bojan remembered it being lowered from his father's train, remembered the darkness inside the box. The dog was much larger than he had expected, almost three feet at the shoulder, with a broad skull, wide feet, and a squashed, painted black face. It had flabby rings of skin that rounded out the bottom of its jaw, and the moment it stepped out of the crate Bojan realised that the experience he had been preparing for – the excited, slobbered greeting; interested eyes peering into his plate at the dinner table; a companionable walk in the park after school – had nothing to do with this behemoth. He slid instinctively behind his father, who reached around and pulled him forward by the sleeve so the dog could smell him.

He remembered thorough scrutiny when the big face came close and the air around him drew in and out of the wet muzzle. He remembered it for years afterwards, the sensation of being uncovered, even though, at that time, he wasn't covering anything up at all, wouldn't know for years that there was anything he should be covering up.

Confined to the yard, the mastiff still dominated the neighbourhood. The family's property stretched from the brick wall along the avenue to the hill behind the house, where the creek cut through a small glen before disappearing into the woods, and here the dog had free rein. It made a show of patrolling up and down the grounds and bounding to the fence whenever the neighbour's widow made her daily appearance. Kaiser had a bark you could hear all along the street, and made use of it often; so often, in fact, that the paperboy made his deliveries from across the road and the local children started taking the longer route to school. Within its first month at their house, the dog had killed two of the neighbourhood's alley cats, communal pets for whom the ladies sometimes left out saucers of milk. Mrs Senka would find them under the front porch, necks wrung, spines stiff and twisted, and she would scramble to pull them out before Kaiser clued in to what she was doing and came to interrupt her disposal of his trophies.

In July, he jumped the fence and made off with the widow's champion pug; two weeks later, an old gun dog that lived at the rest-home two blocks over was seriously injured. People complained, but always indirectly, with reluctance, usually at church and in ways that made their concerns seem more like observations than actual grievances. They knew Bojan's father; they seemed to know better.

Around Bojan's father, the mastiff was keen but subdued, like a retired cannon in a museum. Bojan could picture the two of them on sentry duty: his father, tall and heavy-set, the dog growling like a rusted grate at his side while they performed manoeuvres, or, in some of Bojan's more daring fantasies, searched for mines. This was years before newspaper reports surfaced, years before photographs of barbed-wire compounds and starved men herded into lines. When he saw the two of them together, when his father lowered his half-empty plate on to the floor after dinner, or gave the wadded skin under Kaiser's jaw a firm tug before heading upstairs for the night, the sense of something earned that had passed between them was obvious to him.

Bojan tried, in those early months, to stay out of the mastiff's way, but they inevitably crossed paths: at mealtimes, usually, and every morning when he walked from the porch to the gate, and every afternoon when he walked back, fighting the frantic urge to bolt under its eyes. In the early evenings, when they were alone, the mastiff would follow him inside. It would corner him in the hallway and pin him to the wall with its big, wet face pressed against his, and smell and smell him; then it would take a step back and bark until one of the adults came to call it off: measured, even, ground-shaking barks that made Bojan feel like something inside his chest was going to shake loose, buckle under that sense that he had done something and that the mastiff knew, it knew, it knew, and it was trying to sniff him out.

When he turned 11, Bojan developed his own avenue for dealing with the mastiff. It was an accident, really, something he never would have thought of on his own; he came home one afternoon in late August, the thunderstorm outside bending the willow and shattering branches against the fence, to find the house empty and the dog already inside, waiting for him. He was wet and cold, and the moment he stepped through the door the animal started a low growl that rose in pitch as he stood there, shaking, with his satchel over his shoulder. He wasn't sure what happened. His nerve broke and he bolted: he ran for the servants' room under the stairs. Mrs Senka slept there, kept her pistol in the dresser drawer in case somebody came into the house while his father was gone; as he reached it, he could see the mastiff in the mirror, clumsy on the rugs and hardwood floor, bursting through the door behind him.

The pistol felt tiny in his hand but he gripped it and turned, and the dog skidded to a halt with a dumbfounded look of recognition. Then Bojan, his outstretched hand shaking, said, "Sit." The dog continued to look at him. The alabaster clock on the mantelpiece chimed quietly. Bojan said, "Sit" again, and the dog – an army dog, obedient to a fault – lowered itself reluctantly on to the rug. He could have killed it, at that moment; he would have, he was going to, but when he squeezed back on the trigger the gun gave a sad little click like a lighter out of fluid and he realised it was empty. The mastiff's reaction was surprising: Bojan saw the sound ripple through its body, and the head ducked back, braced for impact, and the dog, finding itself alive long moments later, started to whimper.

That was how it started. His father collected guns – Colt pistols and Winchesters mostly – which he kept in a cabinet in the parlour. The key lay in the bottom of the Chinese porcelain vase in the corner. From that day on, whenever he was alone, whenever the dog confronted him in the yard or coming through the door, he went into the parlour and took down one of the revolvers, the one he had learned to shoot. Then he would say, "Sit" and the command would stretch between them in the silent house until the dog, shaking from head to foot, sat down.

He'd unload the bullets one by one, into the palm of his hand. Then he would point the gun at the dog's head and fire the empty chamber – click! – at two feet, just like that, between the eyes. The sound died in the hallway. More often than not, the dog pissed itself. At other times, it would shudder as though he'd hit it in the heart, and then it would stiffen up. It was quite a sight, the mastiff – a hundred pounds, black square jaws tight with concentration – starting, splitting inside out with confusion. Sometimes he thought it might die like this, he thought he might scare it to death, but it always continued to stare at him as he reloaded the gun and carefully put it back in the cabinet. He was always careful to do it when his father was out of the house.

He would wonder for years whether everybody knew how he would turn out, whether there was something about him that revealed itself to people who could just feel those things, and even to people who couldn't, something about him that made itself obvious to everyone around him. Bojan was 11, shy, and even then he loved music, the only boy at his school eagerly learning piano.

On the way home one afternoon, some boys from a few blocks over wolf-packed him in the park. There were four or five of them, boys he had grown up with, and they knocked him down in the soft mud and pushed his face into the daisies. Some of them wadded handfuls of dirt into his hair. Between their fists and the blades of grass and mud flying everywhere, he saw one of the boys empty his satchel – all his school things, his half-eaten lunch, pages and pages of music notes – on to the ground, then unzip his pants and piss on the papers. For any other boy, it would have been about his name, his father's military rank; or else about money, the new shoes and the car in his father's driveway, redolent of something old and entitled. But with Bojan, it was different.

He went home with his shirt torn and his nose bloodied, the pissed-on pages of his schoolwork abandoned on the ground in the park. Mrs Senka was in the kitchen, fixing dinner. As she was wiping his face and knees clean, beside herself, half-scolding, he put his arms around her and rested his head on her shoulder and held the frayed end of her hair between his fingers. Behind her, afternoon shadows slid across the polished mahogany of the house, and, in the foyer, his father, stooped with something more draining than disappointment, more palpable than rage, stood looking at him from the hallway stairs.

His one coherent thought in the park had been a silent longing for the mastiff, the huge, defensive hulk of it, the alliance he still hoped might shift if the mastiff saw him under attack. This need made him angry. After dinner, when the whole house was still, his father asleep in front of the study fire, he opened the door and let the mastiff in. The night was warm, and the dog's coat smelled of lindens. He led it into the parlour.

"Sit," he said.

He opened the cabinet and took the pistol down, unloaded the bullets. He turned his back to the mastiff while he did it, but he could see the big folded-over squares of its ears, reflected in the glass of the cabinet, rise at the sound of the shells clinking on the wood. He turned around and pulled back on the hammer, and then fired three times in rapid succession – click! click! click! – while the dog shook convulsively where it sat on the carpet. Then he lowered his arms and stared for a long time at the rancid stain spreading over the tassels and ornate trees and Persian birds. When he looked up his father was standing in the doorway.

"Is that how it's done?" his father said.

His father had blue eyes, and a sort of glazed stare that went through you and out the other side. He wore khaki pants and a crocodile-skin wristwatch that had passed to him from Bojan's grandfather, the colonel. The tips of his shoes were like glass.

His father came into the parlour and stood over him. Then he pulled out a chair.

"Sit," he said.

Bojan sat. Across the hall, the mastiff stood to attention, its punched-in face dark and alert. Behind it, Bojan could see the arm of the grandfather clock swinging to and fro, potted ferns sitting on a row of painted elephant stands, the varnished stairwell winding up into darkness. It was one o'clock.

He heard his father's slow, hollow breathing somewhere behind him, above his head, near the cabinet. Bojan heard him pick up the gun – the smooth, metallic scraping as it slid across the sill of the cabinet and into his father's calloused palm – and begin to reload the bullets, one by one. Bojan's head felt heavy and his neck was stiff. The sound of the bullets falling into the chambers was slight and stifling. The french window was open; wind rippled the curtain. His father smelled of wood-smoke.

He heard the last bullet settle, and then the compacted sound of the gun snapping into place, then the hammer falling back. In the hallway, the light was dim and some of the pictures were crooked. Kaiser's tail was wagging.

The blast went off right by his ear, and for a moment his heart felt punched, like someone had swung a hammer directly into his ribs, and the deafening contact of it went through him. The mastiff folded up and fell. It looked almost asleep, lying there, the black face rumpled into the carpet and the stain, darker now, spreading around the big forepaws.

Bojan would wonder, years later, whether his father looked anything like this when they shot him, somewhere by some fetid pond, in an unnamed battle; whether they made him kneel there, in the mud, and whether his face, puzzled for a moment, collapsed on itself when his body did. When he watched Mrs Senka take the folded-up flag, he remembered the mastiff outspread in the parlour, and his father dimming the lights as he went along the hallway until he reached the staircase and went up.

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