Shax died in his attempt on Paige's life, but the Oracle tells the Source that she hasn't solidified her bond with Piper and Phoebe yet. He thus still has a chance to shatter the Power of Three. The Oracle says that it was agreed years ago that every newly minted witch should have 48 hours to decide whether to use her powers for good or evil, the so-called "Window of Opportunity." She suggests that the Source seduce Paige into turning evil. This would be an even greater victory than killing her; not only will the Power of Three be permanently shattered, but he'd have a powerful evil witch on his side. To that end, the Source goes to Shane, still in the hospital recovering from Shax' attack, and possesses him. Paige comes to visit him, still badly shaken. They embrace, and Shane's eyes turn black.
Darryl comes to the manor, asking after Inspector Cortez. Cole shimmers in, and after blasting a couple of bounty hunters, tells that he found Cortez. He also says that he heard gargoyles stirring; he thinks they may be trying to ward off the Source. Leo thinks that if they can find Paige, they should be able to ward him off. However, he still can't sense her.
"Shane" goes to Paige's apartment. Her parakeet, Oscar, seems oddly agitated. "Shane" mentions the case that Paige is working on. Jake Grisanti is suspected of abusing his young son; abusive parents are one of Paige's pet peeves. As Paige turns to leave, "Shane" sends Oscar up in flames.
Cole and Leo find Cortez about to fall into a lava pit. Cole put him there to make sure he doesn't expose the sisters. Cole is unwilling to bring him back, but Leo insists that they let him go. Leo demands that Cortez keep quiet about the Halliwells, and then orbs him back to San Francisco.
Jake arrives at South Bay Social Services with his wife, Carol, and their son. Jake goes to the bathroom, where the Source leaves Shane's body and possesses him. Meanwhile, Paige is asking after the church she was placed, and argues with her boss, Bob Cowan. She is worried about the boy.
Piper walks into Prue's room to find Phoebe standing at the window, crying bitterly. It's the first time she's really broken down since Prue's death; she's held it together for both of them.
Cowan hasn't made a final decision yet on the Grisantis, much to Paige's frustration. "Jake" briefly argues with Paige. Paige heads out for the church. "Jake" goes back to the bathroom, where a custodian is bending over an unconscious Shane. The Source sends the man up in flames and repossesses Shane.
Paige finds Sister Agnes, who placed her for adoption. Sister Agnes tells Paige of her birth parents; they came to her in a swirl of blue lights. Sister Agnes shows Paige her blanket in which she was wrapped, showing the letter P. Her mother had requested that her name begin with P.
Piper has also found the church where Paige was left. She and Phoebe find Paige there and Piper freezes Sister Agnes. Paige walks away angrily, but Piper and Phoebe tell her that she has a power, and needs to learn how to use it to protect herself. Piper tells Paige that in all likelihood, she's a telekinetic like Prue. Paige tries to practice on a candle, but can't move it by waving her hand or squinting her eyes (the ways Prue channeled her power). Paige grumbles that she must be of little account as a witch if she can't move a candle. Just then, the candle disappears in a swirl of orbs and reappears in a shocked Paige's hand. Piper and Phoebe think Paige's telekinesis works differently due to her being half-Whitelighter.
The Source has again possessed Shane and tries to enter the church, but a gargoyle repels him. He falls down in front of the door, but Paige goes to him and they leave. "Shane" blasts Phoebe and Piper as he and Paige walk away.
Cortez is still determined to expose the sisters, despite threats from Cole and Darryl. He calls a surveillance team.
Piper and Phoebe realize the Source was at the church, but don't know why he didn't try to kill Paige. Cole doesn't understand either. Leo speculates that the Source isn't trying to kill her anymore, but instead turn her evil. Cole remembers the window of opportunity, which has less than 24 hours to run.
"Shane" is back at Paige's apartment and is comforting her. Paige is still confused by all that's happening.
Piper and Phoebe search the Book of Shadows to help find Paige; Phoebe calls for "a little help" and the Book opens to a spell that can reveal evil. They don't know where to find the Source, but Leo thinks Cole can find him. Phoebe doesn't understand how that's possible. Cole points out that all demons can sense the Source's presence; it's how he reminds them of his power. He thinks that if he can focus on the Source's aura, they'll be able to find him. Phoebe and Piper cast the spell on a pair of sunglasses. Phoebe puts the shades on and they reveal Cole as Belthazor, startling her. Phoebe thanks Grams for helping them, but Piper thinks "somebody else" may have actually flipped the page.
"Shane" tries to persuade Paige to use her powers for her own desires. He suggests that she use her power to kill Jake. She ends up smashing a mirror. Later that day, Jake and Carol storm out of Cowan's office. Paige follows them, with "Shane" looking on. As they head outside, Paige holds out her hand and calls for Jake's heart. Jake doubles over in pain. Phoebe, Piper, Cole and Leo pull up; Cole sensed the Source was there. Phoebe puts on the sunglasses and sees a black aura around Paige. They rush to Paige and try to snap her back to herself. Paige won't back down, but Piper knocks her hand down and Leo orbs her away. Jake recovers, and it turns out that Carol is the one beating their child.
Piper and Phoebe head home while Cole stays behind to hold off the Source. "Shane" comes up behind Cole, but flames away before Cole spots him. Cole shimmers after him, but before he can make a move "Shane" runs him through with a sword.
Piper and Phoebe find Paige and Leo at the manor. Leo is trying to convince Paige she isn't evil, but Paige is pitching a fit and orbing things at him while trying to escape. Piper tackles Paige to immobilize her, and Phoebe and Leo take her place holding Paige down. Just as Piper is about to check the Book, "Shane" flames in and flings Piper through the banister. "Shane" throws an energy ball at Phoebe, but Phoebe levitates out of the way. While still in the air, she tries to kick "Shane," but he disappears and Phoebe crashes into the grandfather clock. "Shane" reappears, and Piper blasts him. Just as "Shane" reconstitutes, Phoebe puts on the sunglasses and sees the Source. Paige gets back to her feet. The Source tries again to sway Paige, changing in rapid succession into Cowan, then Carol, then the little boy. Phoebe cries out, and the "boy" blasts Phoebe with electricity. Paige shoves the "boy" down just as the clock chimes; the window of opportunity has closed. The Source implies that he attacked Cole. Just then, he spots Cortez with a camcorder, blasts him with an plasma ball and flames away. Leo immediately heals Cortez, replying to Paige's wonder at how he did that by stating that whitelighters heal good people.
Both Paige and Cortez realize fully who the good guys are. The sisters, with Paige, and Leo find Cole. Leo can only heal his human half, but Paige offers to use her power as well. Together, the two heal Cole.
Cortez goes to Darryl and wordlessly hands over the tape from the camcorder, ending his pursuit of the sisters.
The sisters meet at P3, Paige now joining them. Phoebe curiously asks why she attended Prue's funeral. She explains that a part of her felt like she'd lost her too, and somehow felt drawn all three of them. Piper and Phoebe take her to the attic and cast the summoning spell; Paige and Patty meet for the first time.