When the water demon that killed the Charmed Ones mother 20 years ago returns and starts killing again, Prue, Piper, and Phoebe must face him at the same camp where Patty was drowned to death. While there, they meet Sam, their mother's former white-lighter and learn some shocking secrets about their mother, one of which mirrors Piper's relationship with Leo. Prue goes to some drastic lengths to vanquish the water demon.