Mary is a fair-haired Yorkshire livestock keeper with blue eyes and weather-reddened cheeks. Rain roughens the skin around her mouth, and wool grease and hay dust cling to the cuffs of her sleeves. She moves with a careful, economical steadiness, always placing herself between her son and an open door. When frightened, she goes unnaturally still, as if listening for hooves on a road no one else can hear. The unexpected detail is her habit of mending tiny, elaborate paper animals for William, folding them from feed invoices with the patience of a village craftswoman.

Mary's affection is genuine but guarded: she can laugh warmly at Oswin's old stories, then immediately test him on a detail that does not fit. She is tender with sick animals and her son, yet brisk with adults who waste time. In calm moments she is observant and practical; under pressure she becomes stubbornly courageous, though afterward the fear catches up with her.

Mary Hirst was raised in Yorkshire among stone walls, wet pasture, and practical warnings about things best left unnamed. She married Oswin Hirst for the warmth of his stories and the gentle steadiness he showed around animals. He told her he was a wandering adventurer who had spent years on the road; she believed him, and loved the man she thought stood beside her. On their wedding night, something headless occupied Oswin's shape: a body crowned by empty air and two red, saucer-bright eyes. Mary has never been able to decide whether Oswin deceived her, whether a Barguest took his place, or whether both things are true. She remembers the encounter as a consummation and has come to believe that the father of her son William may be that creature. William was born with black hair, unlike his blond parents, and burning blue eyes that recall Oswin's. He is slower to learn than other children, and Mary watches him with fierce tenderness. A later child was sickly and died soon after birth; other pregnancies have failed. Oswin has not seemed to age since they met, and he avoids iron with a reflex no explanation quite covers. Mary keeps iron scissors on her person and an iron thimble near William. At the old seasonal turns she watches husband and son through the night, afraid that fae or demons may claim them. Her father, a Yorkshire man with a distant cottage, suspects Oswin's true nature and wants to turn the secret into an advantage for his family. Mary is caught between her love for Oswin, her terror of the headless presence, and her father's designs.