Seven years ago, the Ballastian sisters' parents left them in the magical Straygarden Place, a house surrounded by tall silver grass and floating trees. They left behind a warning saying never to leave the house or go into the grass. "Wait for us," the note read. "Sleep darkly." Ever since then, the house itself has taken care of Winnow, Mayhap, and Pavonine -- feeding them, clothing them, even keeping them company -- while the girls have waited and grown up and played a guessing game: Think of an animal, think of a place. Think of a person, think of a face. Until one day, when the eldest, fourteen-year-old Winnow, does the unthinkable and goes outside into the grass, and everything twelve-year-old Mayhap thought she knew about her home, her family, and even herself starts to unravel.