On their anniversary of becoming witches Prue, Piper and Phoebe face a bizarre demon who pulls the Book of Shadows into another dimension and begins reversing each spell, causing vanquished demons to return and slowly erasing the sisters powers.

Piper,Phoebe and Paige come to the aid of Mylie, a Mermaid-turned-human on the run from the Sea Hag who in turn needs the mermaid for the evil Necron.In trying to help her,Phoebe is turned into a mermaid,but she refuses to change back...