Christy moves into Billie's dorm room and tries to lay the blame for their parents' death on Piper. Then she heads off to track down the last unvanquishable Noxon demon. The demons at the Magic School are also after the Noxon...to defeat the Sisters. When one of the demons questions their leader Creo, he's killed, and Christy arrives to take command.
Paige is waiting for Piper at the Manor and clearly is eager to help with the demons. Piper figures something is up and tells her to talk to Henry. Paige reveals she's worried about losing her identity in their marriage. Piper figures the Noxon knows who's behind the death of Billie's parents and plan to track her down, and Paige heads into the underworld to find him.
The last Noxon, Pator, is in the Underworld when he's snagged by a creature capable of negating his powers and another demon, Jondar, demands answers from him. Pator reveals he's the only one who knows about the Trinity but his interrogator leaves him there.
Coop is trying to get Phoebe on a date and beginning to be attracted to her himself when Billie shows up looking for someplace to stay after her parents' funeral. Paige finds Pator and tells Piper where he's at, and Christy arrives and tags along to destroy it. Paige would rather question him and Christy dismisses her concerns and they confront Pator. Christy tries to kill him, freeing him, and then tries to invoke the astral spell but Piper interrupts her just in time by knocking her into a rock, and Jondar teleports away with Pator.
They return to the Manor and Christy blames them for letting the Noxxin escape, then walks off and tells them to stay away from Billie. Henry gets hold of Paige who puts him off and asks Phoebe to borrow Coop for some help. Christy meets with Creo who convinces her to get Billie away from the Halliwells. Christy tells him to find the Noxon or they'll need to change his plan.
Jondar considers selling Pator and Pator knocks him back onto a volcanic spire, killing the hunter and freeing himself. Coop is trying to get one of Phoebe's co-workers, Michael, to date her and again it becomes clear he's infatuated with her but he can't according to "the rules." Paige shows up to ask him for help and finally he agrees...by merging them so that Paige is in Henry's head.
At Phoebe's, Michael shows up to woo her while an out-of-sight Coop coaches him. It seems to work but they're interrupted when Christy arrives to accuse Piper of attacking her. She and Billie take off and Billie wants to talk to the Halliwells on her own and heads for the Manor. Henry and Paige have a back-and-forth conversation inside of Henry. They resolve their differences and then Paige orbs them to the Manor so Henry can explain. They need Paige separated to use the Power of Three, but are interrupted by Billie who tries to take the vanquish vial. Paige/Henry orbs it to her but Billie takes it back and leaves.
Billie and Christy goes to Magic School to find a way to track Pator, and Christy checks in with Creo who doesn't know where Pator is, and says she'll have to use her powers. Christy tells Billie she'll listen in on the Halliwells, who are scrying for Pator. It's not working because Paige is inside of Henry, so Phoebe calls Coop to break them apart and she figures out he's interested in her. He separates Henry and Paige and the Halliwells track Pator down…while Christy directs her and Billie to the same place.
The Halliwells get there first and confront Pator, who offers to talk but Billie and Christy show up and demand to kill him. Billie misses with the potion so Christy uses Billie's power to amplify hers and blow Pator up, then escape. Piper realizes this may be the ultimate power they've been looking for.
Phoebe gets back to her apartment to find Coop waiting for her. Phoebe admits she has strong feelings for someone--Michael. Coop is disappointed but covers for it and leaves after Phoebe thanks him.
Paige resolves not to give up on Billie or Christy after all they've been through, but Piper's not convinced. And Christy assures Billie that it's just the two of them…and always will be.