When a family moves into a new apartment in San Francisco, young Robert starts exploring and discovers the empty apartment upstairs. He opens a door and sees a cabin in the woods, with a man chopping wood who beckons to him. Robert brings his younger sister, Jane, to meet "the man upstairs," who expresses an interest in meeting their older sister, Peggy. When Peggy goes upstairs and opens the same door Robert had opened, she only finds a closet. However, strange noises emanating from the empty apartment, and wet footprints in her own bedroom, cause Peggy to visit the apartment again, and this time, she finds a terrifying surprise waiting for her.