He's in your house. He's in your family. Or is he in your mind? Gil has been estranged from his sister ever since her obnoxious son tried to drown his daughter on a family holiday.

That's Gil's interpretation; his sister thinks Matthew was just playing around. Or did. When she and her husband perish in a car crash, Gil becomes Matthew's legal guardian.

Matthew is now an urbane 17-year-old, raised on Manhattan's Upper East Side, a planet away from rural Vermont, where Gil lives with his wife and daughters, teaching at the local university. At first, Matthew appears to have changed, but when he joins Gil's writing class, he submits a story detailing the various ways a character resembling Gil's youngest daughter might die. While Gil believes he has invited a psychopath to live under his roof, the women in his life are impressed by Matthew's intelligence and charm.

Is Gil losing his mind, or are his family in desperate danger?