William is a small, quick-moving child with a habit of occupying the exact patch of floor someone else meant to use. He leans close when curious, then remembers himself and shuffles back with an embarrassed grin. His broad baby teeth are still coming in unevenly; when he chews, he works one side of his jaw with grave concentration, and his laugh flashes a gap where a front tooth recently fell out. He smells faintly of damp wool, apples, and the woodsmoke that clings to his father's coat.

William is open-hearted but not blindly trusting: he will share his apple with a stranger, yet watches that stranger's hands while doing it. He wants to be brave like his father, but when danger becomes real he seeks shelter and feels ashamed afterward. In a playful mood he chatters and invents elaborate explanations for ordinary things; when Oswin is tense, he becomes careful, helpful, and watchful.

William is Oswin Hirst's young son, raised among the ordinary rhythms of a hard-working household: mending, errands, meals, and the comforting sound of his father's return. Oswin dotes on him, but William has begun to recognize the strain behind that affection. One winter evening, Oswin came home shaken and feverish after an encounter with something that stirred the dangerous nature he keeps buried. William reached for his hand, and the lamps guttered out; for a breath, every dog on the lane howled at once. Oswin pulled away as if he had burned his son. William remembers only the darkness and his father's frightened face, but since then Oswin has watched him with a protectiveness that sometimes feels like a locked door. William remains curious about the world beyond home, trades small favors with neighbors, and has recently started asking why his father never lets him walk alone past the old mill.