Terri is looking forward to spending the summer with her new friend Patricia -- that is, until one night, she sees something strange move across the lawn. Determined to discover the scary thing she saw disappear into the woods behind her house, Terri knows she has to head for the lake she's been forbidden to go near. Soon she's in a race against time, as everyone around her starts to change, including her mother, her uncle and her new best friend. In order to save them, Terry must return to the old boathouse and uncover the secrets to the monster-filled lake.