Cole is walking through a dark cavern, with a sword in his hand, when he encounters the Source chanting. Suddenly, the Source pulls off his hood -- revealing Cole's face. The Source tells Cole that he has been reborn within Cole's body and he won't have a choice but to accept that they are one. Just then, Cole wakes up sweating -- it was all a nightmare.
Piper cooks up a big breakfast to celebrate their vanquishing the Source. However, only Leo is there in time. Paige orbs into the kitchen and lands on Piper; she's been practicing orbing from one location to another. She's in a hurry to get to work. Phoebe comes downstairs, somewhat haggard. Leo gets a "jingle" and orbs out. Phoebe tells Piper that she's worried about Cole; she feels like she had some kind of premonition about him, but something was blocking it. Piper thinks it's just cold feet.
The Seer gestures, and a surprised Cole flames into the Underworld much as the Source did. Cole is very angry; he realizes that he is becoming the Source and he doesn't want to. The Seer tells him it was all part of her vision, but the only reason the Source hasn't completely taken him over is his love for Phoebe. But when it does, his powers will shield him from her premonitions. She tells him of Kurzon, one of the Source's old rivals. He is making a move to take over as ruler of the Underworld. Cole isn't willing to go along, but the Seer tells him that he will once the Source has taken him over. Cole flames back out, and finds himself in a bathroom in the manor. He runs into Phoebe, but hurries back out, claiming he has a migraine.
Kurzon is meeting with several of his allies to plan their next move. Suddenly, the Seer appears to him. She tells him that a witch is after him, but if he kills her first, it will all but assure that he will be the next Source.
Paige is offered a promotion to a full-fledged social worker for having helped Carolyn. ("Charmed and Dangerous") In the process, Mr. Cowan passed over another, more experienced assistant. Paige is somewhat unsure about taking it, because of personal gain from using magic to help Carolyn.
Phoebe is staring at Belthazor's entry in the Book of Shadows when Piper comes up to the attic. Phoebe tells Piper that Cole is starting to avoid her as in the days when he was still half-demon. Piper suggests using magic for help.
Paige comes home and tells Piper about the promotion. She's convinced it's a personal-gain backfire. Suddenly, Kurzon shimmers in and throws an energy ball at Paige. Paige orbs it to her hand and throws it back at Kurzon, but misses. Kurzon throws another energy ball at Paige. Paige orbs out of the way, but lands on the floor. Piper blows Kurzon up, but he reconstitutes. Kurzon didn't expect to have to fight two witches, and shimmers out. Piper calls for Leo, who tells them that the Source's death has touched off a major power struggle in the Underworld. Whoever manages to kill even one Charmed One is guaranteed to take the throne.
Piper, Paige and Leo head up to the attic just as Phoebe is casting a spell to hear her heart's desire. An elderly woman and a small girl appear. The woman claims to be Phoebe's future self, and the girl also says her name is Phoebe. She turns out to be Phoebe from 1985, when she was 10 years old.
Little Phoebe is scared out of her wits, despite the sisters' efforts to comfort her. Cole walks into the attic. Old Phoebe slaps him across the face and curses at him. Old Phoebe and present Phoebe head to present Phoebe's room. Paige asks for Cole's help in identifying the demon that attacked them when he suddenly flames to the Underworld again. The Seer tells him the Source brought him there to tell her something. Cole sincerely wants to stay good, but the Seer thinks the Source is getting closer to taking him over. She warns him to get back to the sisters in case Kurzon attacks again.
Old Phoebe and present Phoebe look through a photo album. Old Phoebe is somewhat bitter, saying that she had a lot of promise. Present Phoebe senses she knows something about Cole, but old Phoebe doesn't want to risk changing the timeline. Present Phoebe notices that old Phoebe isn't wearing a wedding ring, and is convinced the spell would not have worked if there wasn't something she was supposed to know. Old Phoebe still isn't willing to say anything.
Little Phoebe is hiding in the corner, and doesn't believe that Piper and Leo are trying to help her. Present Phoebe comes down and tells little Phoebe who everyone is. Present Phoebe also shows little Phoebe her photo album, and little Phoebe recognizes it as a Christmas gift from their father. Just then, Cole comes back in. Little Phoebe is enthralled by him, and present Phoebe tells him he's their fiance. Little Phoebe calls him their "prince." Present Phoebe remembers that Cinderella had been her favorite story as a child. The sisters and Leo go to check the Book, leaving Cole with little Phoebe.
Kurzon comes to the Seer, and is angry that she didn't tell him he was going after the Charmed Ones. He is ready to kill her on the spot, but the Seer tells him that she knows of Phoebe's spell. She suggests that he kill little Phoebe; since her powers are still bound she won't be able to defend herself. Little Phoebe's death will kill present Phoebe as well, permanently shattering the Power of Three.
The sisters find Kurzon in the Book. Leo tells them that he's powerful enough they'll need the Power of Three to vanquish him. Just then, they hear little Phoebe screaming downstairs; Kurzon is back. He throws an energy ball at little Phoebe, but Cole jumps in front of it. The energy ball doesn't even affect him, much to Kurzon's surprise. He recognizes Cole as Belthazor, and is surprised to find him alive. Cole conjures a dagger and throws it at Kurzon. When that doesn't faze him, Cole throws a fireball at him. Kurzon realizes that Cole is now the Source, and shimmers out just as the sisters and Leo get downstairs. They find little Phoebe passed out. She comes to and thanks Cole for saving her.
Little Phoebe doesn't remember much of the attack. Paige nearly blurts out that she's her sister, all grown up, but present Phoebe cuts her off and says she's their cousin. Leo realizes that Kurzon is trying to permanently destroy the Charmed Ones, and orbs little Phoebe away for safekeeping. Paige finds the dagger, but Cole says it's Kurzon's. He also says that he stabbed Kurzon with it and got them enough blood that they can scry for him. The sisters wonder how Kurzon could have known about Phoebe's spell. Cole suspects the Seer told him.
Present Phoebe again tries to get old Phoebe to tell her what she knows about Cole. Even when present Phoebe mentions Kurzon's attack, old Phoebe still won't talk. She goes to the attic just as Piper is copying a spell to vanquish Kurzon from the Book. Paige is scrying for Kurzon, and finds him on the other side of town.
Cole flames to the Underworld and confronts the Seer. The Seer tells him his love for Phoebe is the only thing keeping the Source from taking him over, and without Phoebe he'll be strong enough to vanquish Kurzon himself. Cole says that his love for Phoebe is all that's keeping him alive. However, he refers to himself in third person -- a sign that the Source is taking over. The Seer still wants Phoebe dead, but Cole threatens to kill the Seer the next time she betrays him.
Cole flames back to the manor, and finds old Phoebe waiting for him. Old Phoebe says that she eventually found out Cole was the Source. She not only broke off the engagement, but helped her sisters vanquish him. However, she's spent many years wondering about what might have been, and hopes there's a chance to save him before she tells present Phoebe. Cole doesn't think he can be saved; the Source is starting to overwhelm him. Just then, Kurzon shimmers in.
The sisters just missed Kurzon. Paige scries for him again and finds him at the manor. Piper suggests that Paige orb them back there. Paige doesn't think she can; she's still trying to handle orbing from one room to another. Piper persuades her to try. Paige starts to orb away with Phoebe, but has to pick up Piper as well.
Kurzon knocks Cole down with an energy ball. Cole recovers and throws a fireball, but misses. Old Phoebe helps Cole up. Kurzon shimmers behind them and rushes at Cole with a sword, but old Phoebe jumps in front of Cole -- proving that she still loves him. Just then, the sisters orb in and vanquish Kurzon with the spell Piper found earlier. Old Phoebe, with her last ounce of strength, tells present Phoebe that she has her answer. Leo orbs back in with little Phoebe and tries to heal old Phoebe, but is too late. Old Phoebe and little Phoebe disappear -- the spell has apparently worked the way it was intended.
Paige turns the promotion down; she can't in good conscience use magic to change someone's future.
Phoebe, having remembered Cinderella and seen old Phoebe save Cole's life, decides to marry him. Unknown to them both, the Seer is observing them in one of her visions.