Paige's remembers what she thought was a childhood fairy tale: Turns out Paige was the Evil Enchantress in a previous life. As Evil Enchantress she must conceive a child from the Prince, who is marrying his beloved the next day. When the Enchantress conceives the child, her evil kingdom will reign, killing the Prince. When Paige awakens the Evil Enchantress, and brings her into the 21st century, the Charmed ones must travel back in time to save the future and of Paige. In addition, a shocker demon has taken up residence with the Halliwell's, and the only thing that can vanquish him is the power of three.
Paige has spent the night with her old "friend," Glen, and she tells him about a fairy tale from her past, remembering everything, except the final line. After Piper and Phoebe walk in on her and Glen, Paige decides she has had enough of being a witch, and that she isn't moving in with them because they aren't over Prue's death yet, and only want her to move in to help battle demons, not because they are welcoming her as their sister. On a whim, she checks the Book of Shadows, and finds a spell about the Evil Enchantress. She recites the spell, and her Knight in Shining Armor appears. He follows her everywhere (even work), declaring his love for her, and his intention to not leave her until she conceives a child (per the Evil Enchantress' spell). The Knight picks a fight with a truck driver, forcing Darryl (their friendly detective-friend) to call and question them. Paige feels it is her responsibility to vanquish this demon. In the end, Paige finally agrees to move in, partly because she has seen what the power of three is capable of, and partly because the Evil Enchantress has destroyed her apartment.
After Paige's mishap with her Knight in Shining Armor, Phoebe reads the Book of Shadows, and finds the fairy tale that Paige had recited. Phoebe tells Piper that the Evil Enchantress came into her magic later in life, and is defiant and clever. Phoebe realizes this sounds like Paige, and believes that Paige may have been the Evil Enchantress in a past life. She and Piper go after Paige and the Prince, and the fun begins.
Piper still has not cleaned out Prue's room. Neither Piper nor Phoebe feel they are ready to "pack" Prue up. But with the unwelcome addition of a shocker demon, Piper knows that the power of three is necessary. She wants Paige to move in. She is also getting a little jealous/angry that Leo is spending all of his time watching Paige. Piper also realizes that all of the demons are out to impress the Source, and are showing off by going to the Charmed Ones, and that this is the most important time for the power of three to be united.
Leo is watching Paige night and day trying to protect her from any and all demons. It is Leo who convinces Paige that she must look inside herself and see how powerful she was, and can be, if she taps into her true powers.
Since vanquishing the Evil Enchantress means vanquishing Paige, Piper and Phoebe must be careful. They create a potion that will diminish the powers of the Evil Enchantress. Paige decides she must be the one to vanquish the Evil Enchantress since it was her story, but being of the same mind, the Enchantress finds her and the Prince at her apartment, and zaps her with her power, leaving Paige to be helped by Leo. The Enchantress takes the Prince, and Piper and Phoebe follow her back to the Dark Age, where they get locked up. Paige recites the spell again, only stating that she wants to go to his land, and they are let in. Leo fights off the guard watching Piper and Phoebe, while Paige goes after what is essentially herself. Paige is able to ward off the Evil Enchantress' powers until Piper and Phoebe are free, and they throw the potion onto the Evil Enchantress, ridding her of her powers. When they get back home, they realize they still have one demon to vanquish -- the shocker demon. All that is needed to vanquish him is the power of three, and once Paige moves in, they have it.