Tom had tried to use Avada Kedavdra on himself, once, when he was younger. The older boys had snatched his dead mother's necklace from around his neck and smashed it, and Tom had climbed up to the rooftops of the orphanage, his hands shaking with rage and loneliness. He'd tried three times, half-remembered words in a child's voice, reaching over the wind and the rain - three brilliant flashes of light, turning a chimney-pot into a bowler hat, and a nearby pigeon into a plate of coconut macaroons. But they'd caught up with him, and locked him in a room until he'd promised never, ever to say those words again.

From then on, he tried in secret. Bitterly dispirited when it seemed his child's grasp of magic, all wandless flukes and a few things dimly remembered from the house of his parents, didn't get him any further than cursing his own little finger off. No-one noticed. No-one cared. Mustn't let the Muggles know, and so everyone pretended there was nothing wrong with little dark-eyed Tom, who muttered words in Latin under his breath and thought that magic was real.

Tom didn't care. He had a secret. Because if he could curse a finger off - on the sixth or seventh attempt, maybe, and done without a wand, in one of those embarrassing hiccups of magic that meant he had to sleep separately from the Muggle orphans - then he could teach himself to use Avada Kedavra.

Tom muttered "Avada Kedavra" to himself in his sleep at night, and the plants beside his bed would wilt, just a little.

By the time Tom taught himself Avada Kedavra, he had a phoenix-feather wand and his eyes were haunted. He practiced on his room-mate's familiar, a dull boy called Defoe who had a sleepy rat called Ben. And when Tom finally got it right, brought back the green light he could remember from that night on the orphanage rooftops, centering his heart on the fierce and unspeakable want of death, Defoe had to be moved out of Tom's room, and Tom was summoned before the Headmaster.

The Headmaster alluded to the incident in the orphanage. Tom smiled. He'd started learning Avada Kedavra wanting to use it on himself.

But at some point, in the hundreds and hundreds of dark nights between then and now, he'd changed his mind.