Two centuries ago, in the town of Sparrow, three sisters were sentenced to death for witchery. Stones were tied to their ankles and they were drowned in the deep waters surrounding the town. For a brief time each summer the sisters return, stealing the bodies of three girls so that they may seek their revenge, luring boys into the harbor and pulling them under. Penny Talbot has accepted the fate of the town. But on the eve of the sisters' return a boy named Bo Carter arrives, unaware of the danger he has just stumbled into. Now Penny will be forced to choose: save Bo, or save herself.