When Phoebe starts having dreams about seducing and killing men, Piper and Prue discover that Phoebe is somehow connected to a femme fatale demon called a Succubus. Upon learning that the Succubus is killing and draining her victims in order to reproduce, Prue takes it upon herself to cast a spell where she becomes a man in order to stop the Succubus. While Prue is under the influence of her spell, she encourages Piper to go out with Dan.
Spoilers ahead. Coverage follows the scope labeled below.
Complete story — includes the ending
As a heatwave descends on San Francisco, Phoebe begins to have erotic dreams that end in the killing of her dream lovers. The sisters find out that she is psychically linked, through her powers, to a man-killing sexual predator demon known as a Succubus that drains men of their testosterone. When they cast a spell, hoping to find and then vanquish the succubus, it turns Prue into a man.