Mary has pale, weather-warmed skin and bright blue eyes that seem to keep measuring the distance to the nearest door. Her blond hair is thick and usually braided in a practical coil, though fine strands escape around her temples. She moves with a careful, heel-first tread, as if every floorboard might be listening. Before she speaks, she takes a small breath through her nose and holds it for a beat; when frightened, that held breath becomes a faint, involuntary rasp. Her unexpectedly playful detail is a row of tiny stitched birds hidden along the inside hem of her severe work apron, each one made from scraps of a different old dress.

Mary is tender without being meek: she remembers small kindnesses and will defend her husband from insults, yet watches his hands when he comes home after dark. In a safe mood she is dryly funny and generous with food; under pressure she becomes brisk, suspicious, and fiercely decisive. She wants to believe the man she married, but refuses to let that hope outrank her child's safety.

Mary married the man she loved after a courtship built from shared errands, dry jokes, and long walks home from the mill. On their wedding night, he disappeared into the dark for hours. He returned at dawn with mud on his clothes, an unfamiliar animal stink, and no clear account of where he had been. He later told her a tender, carefully rehearsed story about their first night together. She wanted to believe him, and for years she did. Then their young son began waking from dreams of a great black hound at the window and called the creature his father. Mary confronted her husband, who confessed that something had happened that night but still will not tell her what. She loves the warm, familiar man she remembers and fears the thing she glimpsed outside their shutter: a huge dog-shaped shadow with a human way of watching. Now she believes the Barguest may be her son's true father, or at least the presence that marked him. Oswin Hirst, an old connection of her husband's, has begun asking questions about the child and the wedding night. Mary is trying to keep her family together while deciding whether the truth will protect her son or draw the creature closer.