Nothing lasts forever. Not Christmas, with its bright lights and spangled promises of good things that never quite come to pass. Not the dreams of magic that it conjures for children everywhere. Not even Krampus, with his sack of coal and his cold heart. Even villains grow old and achy, age softening their sharp edges, allowing things akin to nostalgia and loneliness to seep to the surface.

It made him wish that the mountain had not been hollowed out, like a sponge, full of tunnels and caves and oubliettes, designed to deter or trap any intruders. Designed to keep Krampus hidden, deep inside the mountain, where he could keep his lists of naughty children and plan his cruelty for the year to come. For if there was someone to seek him, they would never, ever find their way.

And if they did, what would they find? he asked himself, stroking his whitened beard and staring into the fire. Nothing but a sad old bovine, hiding himself away from the world. Disgust welled up inside him like bile. How was it that age had snuck up on him? He could not remember ever having been anything like a child . . . Then again, his type—oh, yes, there were others like him, though they went by different names, in different forms—lived a long, long time.

But nothing lasts forever. Castles crumble, wishes fade, even the oldest of the trees in the woods on the mountain above die after thousands of years.

“Then you must make it last!” he said to himself, rising from his chair and ignoring the knotty pains in his back. He took to pondering how he might do so while wandering the passages that curled around on themselves. Occasionally he stumbled across the remains of young daemons who liked to climb up from the deep fire pits to try to fight him. Even they could not find their way out into the world or back to Hell, once they were lost in Krampus’s labyrinth.

He also stumbled on other things, too, the sort that he had thought hidden for all time. Long-lost memories of a young boy, trying desperately hard to hide his hoofed feet from the other boys in the town. A broken silver fob-watch, its face studded with tiny rubies like drops of blood, lid carved with words in an old language he could not understand. And, in the darkest, farthest corner, where he could not remember having been before, a cloche jar that covered something shrivelled and desiccated. In the candlelight, he thought it looked a bit like a heart. As the flame flickered, he could have sworn that it gave a one feeble beat, then another.

Without knowing why, he lifted the glass gently and picked up the heart. It was warm. He lifted it to his lips, and swallowed it whole. A baby’s cry, thin and hollow, echoed through the hallway, dying away as a bitter wind blew through behind it. And, with that, Krampus knew what he must do—how he could indeed make his story go on forever. He walked through the tunnels, up the thousands of ancient stone steps, exiting through the huge fireplace of the abandoned castle topping the mountain in which he lived. Slowly, as the snow fell and winter bit the air with its sharp teeth, he set out, stumping across the late winter lands in search of his successor.

Hundreds of miles away, the girl Lulah, only ten years old and small for her age at that, set out in her mother’s only winter coat and shoes stolen from the general store in the raggedy strip of shops that had once been a village. She would need them, she knew, but it also didn’t hurt to have added another crime to her short list. Theft, though, was a small thing compared to what she had come to think of as the necessary mischief. Lulah had had to do something impressive to show Krampus she was capable of more than plain disobedience.

The stories her mother had told her about him were supposed to scare her, she knew. Instead, they had left her with a little kernel of hope that warmed her, despite the old shack they called home, the pinching hunger,