A small, sharp-featured boy with black hair that sticks up in damp curls and vivid blue eyes that seem to hold a coal's inner glow when lamplight catches them. His skin is weather-chapped across the nose and knuckles from roaming outdoors, with a faint, persistent flush at his ears even in cold weather. He moves in sudden starts, stopping dead to inspect a beetle or a crack in a wall, then darting off as if pulled by a thought nobody else heard. His breath fogs faintly on warm days when he is upset. The unexpected detail is that he is fiercely proud of his collection of pressed flowers, each kept between scraps of old paper in a wooden box.

William wants to be brave and independent, yet he seeks reassurance whenever the world becomes too strange. Around adults he trusts, he can be candid and unexpectedly tender; among teasing children, he acts bolder than he feels. He is fascinated by frightening things at a distance, but startled by them up close, and he dislikes being treated as a baby almost as much as he dislikes being left alone.

William grew up on the edge of a hamlet where his parents work hard and love him, but have no explanation for the strange little disturbances that follow his moods. As a toddler, he could find a lost lamb by following what he called its 'bright smell.' Once, after wandering into a marsh during a summer storm, he came home dry while every dog in the hamlet hid beneath its master's bed. His parents dismissed these things as childish stories. Oswin Hirst, who spends time with him, has noticed that iron makes William uneasy and that certain flowers turn their faces toward him when he passes. Oswin recognizes signs of mixed hellish and fae inheritance, though he has told no one outright. The formative event came last winter, when a frightened William shouted at a pack of dogs chasing him; every animal stopped at once, and for a heartbeat their eyes shone blue like his. Since then he has tried to be careful with his anger, while privately wondering whether the dogs obeyed him or feared him. Now he wants to prove he can be trusted with the small errands adults keep taking away from him.