Piper arrives at home where we find out that Billie has rescued Christy. Billie drops off some food to her sister, and she warns, "They're coming."
The sisters compare notes and wonder who Christy is speaking about. They want answers but Billie is reluctant to confront her. After she takes off, one Simon Thaddeus Reginald Marks, a witch from a family of witches, shows up to take Paige as his wife.
Demons are torturing one of their own to find out what happened to Christy – they're part of the clan that guarded Christy on behalf of "the Triad." They figure the guardian has been breached and kill him, and then go to find the witch who took Christy. Meanwhile Simon presents his credentials and claims they are destined to wed, but Paige is not thrilled. Marks is not thrilled to hear he has mortal competition in Henry. He goes to visit Piper and make his case to her but doesn't have any better luck. Distracted, she pulls out and bumps into a van driven by…Greg, the hot fireman (from "Chris-Crossed"). While Billie tries to get through to Christy, Henry visits with Paige and insists he should be involved in the dangerous side of her life. Paige is skeptical but relents and Piper arrives to be brought up to speed and talk about Greg. Christy has a panic attack and warns no one can stop "them" from coming…now.
Billie brings Christy downstairs and the demon cult-guardians attack. A battle breaks out and Henry is hit by a deflected fireball. The demons fade out while Christy screams and sets off a fire with her power. Paige attempts to heal Henry and then she and Phoebe send Piper off to deal with her personal problems, insisting they can handle it. Christy apologizes to Billie while the guardian-demons worry they must recover Christy before the Triad find out, then decide to summon the Triad to recover her.
Greg comes to visit Piper and offer to set up her up with his friend to fix her car, notices the burning cookies, and offers to watch Wyatt. Simon teleports in and mistakes Greg for Henry and Paige bursts in and hauls Simon off to read him the riot act. But when she heads up to the attic to help Phoebe scrye, she admits he has a point about endangering mortals. Meanwhile Simon meets privately with Henry for a private chat.
The demons summon the Triad who are not happy. Their leader, Asmodeus, advises caution but the head demon tells them about the Charmed Ones and how they and the Triad both need Christy to go up against the sisters' power. Billie helps Christy to bring forth her powers under her control, with some success. Simon tries to convince Henry that he's interfering in Paige's mystical destiny and at some point Paige might not be able to heal him. When Henry refuses to yield, Simon challenges him to a duel.
Piper and Wyatt are with Greg at his firehouse and he gently wonders about where Leo might be – she affirms that Leo is coming back. She makes an excuse then Phoebe contacts her to warn that the low-level guardian demons are heavily protected by some greater magic. She's interrupted by Billie's screams and she and Paige go to put her out while Piper leaves Wyatt with Greg and heads back to the manor. Billie relates that Christy departed with one of the demons.
Billie relates that she was training Christy when she heard voices about her being the "the Key" to ultimate power and then changed into something dark and the demon showed up. Phoebe figures Christy contacted the demons but Billie doesn't believe it. They're interrupted by Henry calling Paige for help about his duel. She leaves to find Simon telekinetically dueling Henry with crowbars. Henry is totally outclassed as Simon bounces him around. Henry proves he knows about and cares for Paige, then sucker-punches Simon who takes off in defeat.
Up in the attic, Billie gets a telepathic message from Christy to use a reverse of the "to call a lost witch" spell for only Billie to come to her. The sisters give Billie five minutes and she goes to Christy, who confronts her along with the guardian demons. Christy attacks Billie along with the other demons and Billie defends herself then tries to persuade Christy to come around and combine their powers. She gets through to Christy, who summons a huge fireball which Billie then telekinetically blasts into the remaining demons. They teleport back to the attic and Billie says that it's over.
Henry has Paige take them to the top of the Golden Gate Bridge and questions if Paige loves him, then proposes. Paige agrees. Greg shows up to return Wyatt and Piper still insists she will wait for Leo, who is coming back. Christy and Billie go over their family album and Christy apologizes. Billie vows no one will take Christy away again while Phoebe eavesdrops on their conversation. Paige warns that they'll have to wait and see concerning Christy. At Magic school, the Triad appear and state that "she's in position" and they're almost there.