Cole is preparing to be crowned as the new Source, which will give him the full powers of the Underworld. A wizard is outside, the last one left alive. He conjures an illusion of one of the guards and fakes an arrest. The wizard says he is here for revenge and escapes. He tries to grab the Grimoire, a sort of evil Book of Shadows that only evil beings can touch.
Paige and Piper are not sure how to tell Phoebe that Cole has turned back to evil. While Paige is convinced Cole is a demon again, Piper only thinks that Cole is working with demons. They visit Phoebe at her and Cole's apartment. Phoebe tells them that she's pregnant. Cole returns home and Phoebe hasn't told him she's pregnant, so Paige orbs herself and Piper out, not having told Phoebe of their suspicions about Cole. Cole has brought lunch, but Phoebe has to run back to work; she's on a deadline. Cole can tell something's up. Phoebe admits she's pregnant just as the elevator door closes.
At the manor, Piper and Paige are concerned that Phoebe's baby might be a demon. Piper initially doesn't think Phoebe is in any danger; Cole couldn't bring himself to hurt her even when he was Belthazor. Just when they're seeking Leo's opinion, the wizard runs into the manor, pursued by one of the Source's guards. The guard vanquishes the wizard, and Piper blows the demon up. Suddenly, the wizard appears in the manor--as it was all an illusion. He tells them that he wants revenge on the Source for killing his kind centuries earlier. He also tells them the Source isn't dead--but was reborn into a new body and is due to be crowned tonight. He wants Piper, Paige and Leo's help to steal the Grimoire. The Source must lay his hand on the Grimoire as he takes his oath or he won't get his full powers. Leo goes to warn the Elders.
Julie shimmers into Cole's apartment while he's looking for baby things online. He tells her that Phoebe is pregnant and wants to keep up appearances. Julie tells Cole that she's worried about Phoebe's influence on him--and it'll only grow during her pregnancy. Julie suggests that Cole dump Phoebe and make her his queen instead.
Phoebe is trying to string together a new column; her old one got spiked at the last minute. Paige arrives and tells her that the Source has been reborn, and they need her to stop the coronation. Phoebe wants to warn Cole, but Paige tells her that she met the vampire who attacked her through Cole, and that Cole has turned back to evil. Phoebe finds it hard to believe. She goes back to the apartment and only finds Cole, decorating the bedroom with balloons, baby stuff, and flowers; everything seems normal.
Piper isn't happy that Paige told Phoebe of their suspicions. The wizard has created an illusion of the coronation site. The wizard wants to distract the guards, Piper and Phoebe will keep everyone else busy, and Paige will grab the Grimoire. Phoebe comes back to the manor and agrees to join her sisters in stopping the coronation.
Final preparations are underway for the coronation when the wizard shows up. The guards chase him. Cole flames away just as the sisters orb in. Piper blows up one of the guards, while Phoebe engages another. The dark priest telekinetically knocks Paige to the ground. The wizard creates an illusion of Cole to throw the guards off the scent, then zaps them with his staff. Phoebe finishes off one of the guards, while Piper blows up the dark priest. Phoebe spots a guard about to ambush Paige with an energy ball and points him out. Suddenly, a stream of fire shoots out of her hand and vanquishes the guard. Paige orbs the Grimoire into a magic sack. The sisters orb out, while the wizard flashes out behind them.
Back at the manor, Piper wants to destroy the Grimoire. Phoebe is worried; her new flame-throwing power didn't feel right to her. Piper isn't concerned, since Phoebe's past self could throw fire as well. Phoebe reminds Piper that her past self was evil. She wants to talk to Cole about it.
Cole smashes his fist through a window in anger. Julie shimmers in; she already knows the Grimoire has been stolen. Cole wonders how Julie could possibly know when the Seer shimmers in; she was the one who told Julie. The Seer tells Cole that she's concerned Cole's human half is growing too strong. Julie offers to "try again," and Cole realizes that she was really there to seduce him away from Phoebe. Julie again asks Cole to make her his queen, but Cole turns her down. The Seer sends Julie away and tells Cole that his love for Phoebe could cost him everything.
Just then, Phoebe arrives, and the Seer shimmers out. Phoebe tells Cole about the flame-throwing and her worries. He tries to reassure her, but she touches him and has a premonition. She sees Cole throwing fireballs, working with the Seer and other demons, killing demons and flaming. Phoebe realizes her sisters were right all along--Cole is a demon. Horrified, she runs out of the apartment.
Piper has tried several potions on the Grimoire, but none of them have worked. The wizard suggests keeping it, but Piper and Paige won't hear of it. Just then, Phoebe arrives at the manor and tells her sisters that Cole has turned evil again. Leo orbs back in, and tells the sisters that this wizard might not only be evil, but could be trying to become the new Source and use his new powers to revive his people. Leo and the sisters rush in to confront the wizard, but he disappears along with the Grimoire.
Cole is getting ready for the coronation, but is worried that Phoebe knows he's a demon again. The Seer tells him not to be concerned, but Cole wants to find her. The Seer doesn't want Cole to risk being killed by the wizard, but Cole is apparently willing to die, or at the very least get the Source out of him in order to get Phoebe back.
The sisters and Leo are at Cole's apartment, but Cole isn't there. Julie shimmers in. She tells Phoebe she can't allow her to turn Cole back to good, and throws an energy ball at her. Phoebe levitates out of the way and throws fire at Julie. Julie cartwheels out of the way. Phoebe throws fire at Julie again, and this time pins her against the wall before vanquishing her. Piper and Paige are very alarmed; unlike earlier, Phoebe took great pleasure in the kill. Leo says that fire throwing is an upper-level demon's power, further worrying Phoebe. Suddenly, she shimmers to the underworld. The Seer is waiting, and tells Phoebe that she summoned her there. Phoebe tries to vanquish her with fire, but it doesn't even scratch her. The Seer tells Phoebe that Cole is the new Source, and needs Phoebe by his side.
At the coronation site, the wizard attacks Cole. However, Cole has been expecting this, and easily bests him. Cole tells the wizard that he knows what he really wants--his powers. Back at the apartment, the wizard is leafing through the Grimoire, proving that he is indeed evil. The wizard and Cole perform a spell to transfer the Source's power to the wizard. The Seer shimmers Phoebe into the apartment, where she vanquishes the wizard before the spell is complete. Piper, Paige and Leo orb in, but to their horror Phoebe picks up the Grimoire. Phoebe tells them she's embraced her new destiny, and she and Cole flame away. The Seer announces to Piper, Paige and Leo that Cole is the new Source--and Phoebe is his queen. Piper and Paige threaten to vanquish the Seer, but they can't without the Power of Three. The Seer shimmers out. Leo can't sense Phoebe. Piper wants to go down to stop the coronation, but they need the wizard to find it.
The episode ends as Cole approaches the Grimoire to take his oath, with Phoebe by his side.