The Fourth Sister/Plot

Plot
Aviva sits in a darkened room surrounded by lighted candles. She chants and Kaliappears in a mirror. Aviva has been studying the Charmed Ones at Kali's instruction. Aviva reaches for the mirror and Kali grants her a power. Aviva conjures KaliKali tells Aviva to go to the sisters. As Aviva leaves, flames shoot up behind Kali, and her eyes turn fiery red.

Kit has gone missing for several days. Leo looks up the fireplace for her while Piper checks him out. Phoebe walks into the living room and also eyeballs Leo. Piper offers Leo a snack, but Leo wants to puts out flyers the sisters have printed up for Kit. Aviva sees one of the flyers and sets it on fire just by looking at it.

Piper brings Leo a snack just as Prue and Phoebe come downstairs. Leo is painting a wall. Phoebe tries to hit on Leo. Prue notices, and pulls Phoebe into the kitchen. Prue knows that Piper is falling in love with Leo, and suspects Phoebe is trying to steal him away like she believes Phoebe tried to steal Roger. The girls check out Leo's "Bottom".Piper comes in, and Phoebe asks if she thinks she steals their boyfriends. Piper accuses Phoebe of stealing one of hers back in high school. Prue heads out to get ready for a night with Andy and reminds Piper and Phoebe that she wants the manor to herself tonight. Piper and Phoebe agree to a friendly competition of sorts for Leo's affection.

Aviva is writing in her diary when her Aunt Jackie walks in. Aviva is staying at Aunt Jackie's place while her mother is in rehab, and Aviva is upset that Aunt Jackie won't call or visit her. Aunt Jackie, in turn, doesn't understand why Aviva is so hostile to her.

Prue and Andy look through a video store for a movie. Andy is increasingly frustrated that they can never have any time with each other before something comes up that calls Prue away. Aviva brings Kit back.Aviva summons Kali again. Kali tells Aviva she must get the sisters to accept her into their coven. The closet door opens and Kit is there. Kali tells Aviva to take Kit back to the manor.

Piper walks in on Leo finishing up and asks him if he wants to go see a movie. Aviva arrives with Kit; she claims to have found her two hours ago and fed her before coming over. Piper offers a reward, but Aviva declines. Prue and Andy walk in. Prue offers to pay Aviva, but instead Aviva blurts out that she wants to talk about magical stuff. The sisters try to shoo Aviva out, but Aviva instead makes Andy's popcorn tray start popping. Piper freezes the room but Aviva doesn't freeze. Aviva wants to try a spell with Phoebe.Aviva wants to explain, but the sisters aren't interested. Prue brusquely orders her out. Aviva sets the tape Prue is holding ablaze and walks out just as the room unfreezes and popcorn blasts out all over Andy and Leo.

Kali doesn't seem surprised that Prue shooed Aviva out. She thinks that Phoebe will be more understanding, however. Aviva is a bit nervous, but Kali reminds her that she was the one who wanted a family. In return, Kali wants to be able to tap into the magic of the Halliwell line.

The next morning, Prue tries to patch things up with Andy, and talks him into coming over that night. Prue visits Aunt Jackie.Prue is still very angry at Aviva, but Phoebe points out that Aviva did bring Kit back. Prue suspects Aviva might be a warlock, but Piper points out that Aviva didn't freeze, which means she may very well be a good witch like them. Prue is still suspicious, and points out she might very well be evil. She talks Piper and Phoebe into keeping their distance from Aviva until they can find out more about her. As Prue and Piper head for work, Aviva calls Phoebe.

Later that day, Phoebe and Aviva meet at Aviva's school. Aviva cuts the rest of the day and offers to tell Phoebe about herself. Leo comes to Quake to show Piper some samples of the stain originally used on the manor doors. Piper pays for the meal. Leo wonders if Phoebe works there, but Piper scoffs, suggesting that Phoebe is a lesbian.

Later that night, Phoebe is showing Aviva around the manor. Phoebe tells Aviva that she and Piper are fighting over Leo. Aviva suggests that Phoebe tilt the odds by casting a spell on Leo. Phoebe wonders how Aviva knows that the sisters are witches. Aviva tells Phoebe that she's being trained by a high priestess. Phoebe wants to meet her, and they go up to Phoebe's room. Kali briefly appears in the mirror. Aviva has Phoebe touch a dead plant, and it comes back to life. Prue walks in on them and is angry to see Aviva there. Aviva tries to drive a wedge between Prue and Phoebe. As Phoebe tries to calm Prue down, Andy arrives; another night is ruined. Phoebe taking the attack meant for PrueThey agree to try again at Quake the next day. Aviva walks out.

Kali thinks that they'd have lured Phoebe to their side if Prue hadn't been around. Aviva is angry at Prue. Just then, Aunt Jackie barges in; she found out Aviva cut school and wants some answers. They argue, and Kali gestures, causing several candles to flare up. One of them sets Aunt Jackie's dress on fire. Aunt Jackie tries frantically to smother the flames, but falls down the stairs and is knocked out.

While the paramedics tend to Aunt Jackie, Kali tells Aviva to go back to the sisters. She's convinced that Phoebe is already on their side, and Piper will easily be won over. She wants Aviva to kill Prue and take her place in the Power of Three. Aviva goes to the manor and convinces the sisters to let her stay the night, promising not to use any magic. Kali possesses AvivaAviva is sleeping with Phoebe in Phoebe's room. Kali appears late at night and tells Aviva to go after Prue. Aviva tries to slip into Prue's room, but Piper finds her just as she raises a fireball. Aviva says she's looking for the bathroom and walks away.

The next morning, Prue visits Aunt Jackie in the hospital. Aunt Jackie tells of the strange chants and rituals that Aviva indulges in. At Quake, Piper can't reach Prue, even though Andy is there waiting for her. At that moment, Prue is in Aviva's room and finds Aviva's diary, and reads about her and Kali's plans to take over the sisters' coven. The Charmed Ones vanquish KaliPrue calls Phoebe and tells her to call Piper, and to not let Aviva out of her sight. Aviva feigns exhaustion and goes up to Prue's room. Leo is sanding down a corner in the foyer, and wonders if Phoebe and Aviva are in a relationship. Phoebe scoffs, and suggests that Piper is on medication. She picks up Aviva's jacket and gets a premonition of Aviva throwing a fireball at Prue. She rushes upstairs, and Aviva throws a fireball. It hits Aviva's jacket and sets it ablaze. Horrified at what she has done Aviva runs out the door.

Phoebe is slightly burned on the arm. Prue, Piper and Leo are tending to her. Phoebe says that her sweater got too close to one of Aviva's candles. Leo heads out to get an estimate on his work. Phoebe tells Prue and Piper what really happened. Prue tells them that she thinks Kali is an evil spirit that is using Aviva. The sisters head for the attic.

Aviva is packing her witch stuff in a backpack; she doesn't want to use her powers anymore. Kali offers to leave if Aviva touches the mirror; instead, she possessesAviva. As a friendly gesture, they give Aviva a dressThe sisters find Kali in the Book of Shadows. She is an evil sorceress who appears in reflections, like mirrors. She uses innocents as pawns to kill witches and take their powers. The only way to vanquish her is to "shatter her reflection." At that moment, Kali, in Aviva's body, enters the attic and throws fireballs all over the place. Aviva momentarily gains control only long enough to shout for help before Kali takes control again. Phoebe suggests that Piper freeze Kali. Piper is skeptical, since Aviva can't freeze. However, Phoebe thinks that Kali will freeze. Piper freezes Kali, ejecting her from Aviva. Prue flings Kali into a mirror, and Phoebe smashes it, destroying Kali.

The sisters give Aviva one of Prue's old dresses. Aviva admits she's going to miss her powers. Phoebe swears Aviva to secrecy.

Andy is angry with Prue, and refuses to talk to her.