Eleanor has not seen or spoken with her family in years, not since they sent her away to Saint Brigid's boarding school. She knows them only as vague memories: her grandfather's tremendous fanged snout, the barrel full of water her mother always soaked in, and strange hunting trips in a dark wood with her sister and cousins.

When Eleanor finally returns to their ancestral home on the rainy coast of Maine, she finds them already gathered in wait, seemingly ready to welcome her back with open arms. But a strange and sudden death rocks the family, and in order to keep the family that abandoned her from falling apart, Eleanor calls upon her mysterious other grandmother from across the sea.

Grandmere brings order to the chaotic household, but that order soon turns to tyranny. If any of them are to survive, Eleanor must embrace her strange family and confront the monstrousness lurking deep within her Grandmere – and herself.