Phoebe and Cole pursue a demon that is hunting witches. He's already killed two; according to Leo, the Elders are very nervous. Piper and Paige ponder Piper's future hopes to have a baby while Paige consults the Book of Shadows. She thinks she's found the demon she is looking for—but it's Belthazor. A demon attacks Phoebe, and Cole blasts him with an energy ball. The demon blows up, splattering Phoebe and Cole and catapulting them across the alley. Cole asks Phoebe to marry him, much to Phoebe's surprise. Cole wants to talk about it when they get back to the manor, but Phoebe is focused on tracking down the demon. Cole shimmers out to find out more. Piper wonders what happened, but Phoebe is reticent with the details.
In an alley, a demon kills a witch with an athame and takes a charm from her neck. The demon bears a striking resemblance to Belthazor, but this demon's skin is black, not red. He then morphs into a human and calls 911. Another man asks how long to use the phone, and the demon kills him with an energy ball.
Phoebe ID's the demon in the Book of Shadows; it's a Scavenger Demon. Phoebe finally tells Piper that Cole proposed to her, and is surprised she didn't at least get a premonition about it. Phoebe isn't sure what to do; she never envisioned herself marrying anyone. Cole shimmers back in; apparently the killer is just another upper-level demon trying to build his reputation by bumping off witches. He assures Phoebe that he really does want to marry her, that this didn't just come out in the heat of battle. Downstairs, they hear a baby crying; Paige brought a mechanical baby from the clinic.
Leo orbs in; a third witch has just been killed. The sisters call Darryl and proceed to the crime scene. Piper notices scorch marks on a nearby wall—all that's left of the man that the demon killed earlier. Darryl pulls out a necklace the victim was wearing—a necklace with a triple crescent charm. Paige recognizes it as an ancient Wiccan symbol—a sign that she was part of a coven. Assistant district attorney Sykes is questioning the victim's friend, Susan Coleman. It turns out that Sykes is the demon. Phoebe notices that Susan is wearing a necklace similar to the victim's. She goes up to Susan and reveals that she's a witch as well. Susan reveals that she and her friend, Kari, were part of the same coven. Phoebe has a premonition of Susan being killed by the Belthazor-like demon in an arboretum. Sykes shoos them away.
The sisters and Susan go to the site of the premonition. While Phoebe disguises herself as Susan, Piper will freeze the demon and Paige will cut off some of his flesh for a vanquishing potion. The sisters have Leo orb Susan to Paige's old place for safekeeping. Sykes, in demon form, shimmers in and attacks Phoebe. Just as Piper is about to freeze Sykes, a woman, Emma, shows up and throws an athame at him. Sykes shimmers out.
At the manor, Emma tells the sisters that a demon killed her fiancé, a witch named Andrew, a year and a half earlier. She knows that this particular demon doesn't kill just one witch, but the entire coven. Cole recognizes the athame used by Andrew's killer; it's used by the Brotherhood. The sisters vow to get justice for Emma.
Sykes wants to see all of Darryl's recent case files. In his office, he asks Cole's former Shadow Demon, who now works for him, to stand watch before he lures Susan to his office.
Leo tells Susan that he's talked to her coven's Whitelighter, and they both think that she and her compatriots need to lay low until the demon is dead. Just then, Sykes calls Susan and asks her to meet him at his office.
Emma scries for the demon, and finds him—at the manor.
Susan goes to Sykes's office with Leo. Just as he closes the door, Leo spots the Shadow Demon slipping inside. Smelling a rat, he orbs into the office just as Sykes is about to kill Susan. Leo knocks Sykes out and orbs out with Susan. Cole rushes downstairs and tells Phoebe that the demon isn't anywhere to be found. Just then, Leo and Susan orb in and reveal that Sykes is the demon. Just then, Sykes shimmers in and tries to ambush them from behind with an energy ball, but Phoebe spots him and they duck away just in time. Cole throws an energy ball at Sykes; it hits Sykes full force but doesn't even scratch him. Sykes assumes his demon form. Piper freezes him, and Paige gashes off some flesh from his arm. Sykes unfreezes and decks Paige. He throws an energy ball at Piper and Emma, but Cole shoves them out of the way and it smashes the mechanical baby. Cole turns into Belthazor, and the two demons trade energy balls before Sykes shimmers out. Emma is upset, however, because the demon who killed her fiance was not Sykes, but Belthazor.
Emma is horrified that the sisters are protecting Cole, and isn't swayed by their assurances that Cole isn't the same Belthazor who killed Andrew. She storms out. Cole admits killing Andrew, but doesn't even remember doing it; he was just another witch that The Source wanted dead. He suspects that if Sykes has emulated him as well as it appears, he may have to turn fully demonic once again in order to kill him. He asks Phoebe to be ready with the Belthazor vanquishing potion just in case his demonic side overwhelms him.
Piper and Paige make the vanquishing potion for Sykes. Paige adds the portion of Sykes' flesh, and it blows her off her feet—just like what happened to Piper a year earlier when they were making the potion for Belthazor. Cole walks in. Paige isn't at all happy to learn that Cole killed a man, but Piper assures her that Cole is good now. Cole thinks the sisters will need his help to find Sykes. He suspects that if Sykes is really emulating Belthazor, the sisters are next on his hit list. He wants to go to the mausoleum to recuperate from the earlier battle, but suspects Sykes will have set a trap for the sisters. Piper thinks he should come with them anyway to identify any trap.
Phoebe tries to calm Emma, but she won't listen. Emma asks Phoebe if she ever lost someone to evil. Phoebe remembers what happened to Prue.
Cole, Paige and Phoebe go to the mausoleum. Just as Cole suspected, Sykes has set a trap. Paige is surprised that Sykes isn't lying in wait. Cole realizes that Sykes is after him, not the sisters, and the best way to him is through Phoebe.
Sykes ambushes Phoebe at the manor and ties her up in the attic. Piper, Paige and Cole come in just minutes later. Cole finds Sykes and Phoebe in the attic. Phoebe realizes she's merely bait, but Cole isn't willing to risk it. Sykes realizes this as well, proving just how well he's modeled himself on Cole. Cole turns into Belthazor. Sykes assumes his demonic form. The two fight, and Sykes seemingly gets the better of it before Belthazor goes fully demonic and gains the upper hand. Piper and Paige rush in, and Piper freezes the room so they can untie Phoebe. The two demons unfreeze, and Belthazor kills Sykes with his athame. However, just as he initially feared, he can't turn back into Cole and starts to go in on the sisters. Emma rushes upstairs with a potion Phoebe had in her purse. She throws it at Belthazor—but it turns out to be a power-stripping potion, leaving Cole fully mortal.
Piper and Leo now have second thoughts about children, given what happened to the doll.
Phoebe is pacing in her room when Cole walks back in. He'd gone out for a walk and wanted to come back, but forgot he can't shimmer any more. Phoebe says that she still loves Cole, but isn't willing to marry him just yet.