In the teaser, Leo is being taunted by Barbas. Leo tells him he will kill him for helping Gideon. He chases Barbas, but ends up running into an Elder friend, Zola. Barbas tricks Leo into thinking Zola is not on his side and Leo throws Zola against a wall. Leo does stop before doing any serious damage and Barbas is disappointed that he couldn't get Leo to kill Zola.
Zola goes to see Phoebe and Paige at home and tells them Leo tried to kill him. He also says that not all Elders are bad. Zola tells them that if they don't stop Leo from his obssession with killing Barbas, the Elders will have to punish him. He also says there's this big powerful threat coming and they need Leo and everyone else they can get on their side.
Leo orbs to the Book of Shadows and looks through it as someone comes up behind him.
Paige comes up with a plan to stop Leo. She tells Phoebe they should guilt Leo into going to the wedding with Piper. And that they should go after Barbas instead.
Phoebe manages to get Piper and Leo to the wedding and once they are there, Piper and Leo are touched by the love ceremony and share a moment together.
Barbas is in the Underworld trying to get some demons to help him. They don't want to when they find out he wants to go after the Charmed Ones. Barbas tells them they must go after the baby so that Leo's instincts will kick in and he will make a fatal mistake. Then the Charmed Ones will be without his protection. Barbas seems to be winning over the demons. Some creature cloaked the lair to hide Barbas from Leo, and now Barbas says they have a powerful friend to help them.
Paige finds out the Magic School is closing down now that Gideon isn't around to keep it going. Paige says she will fight to keep it going.
There's an incident where inspector Sheridan comes upon Leo and Paige. She draws her gun on them and Leo uses his power to throw her across the room into a wall, knocking her out. Darryl is stunned and wonders if Leo's gone crazy. Phoebe says he might have.
Then we're on the same bridge as in the teaser. Only this time, when Leo comes upon Zola, he kills him as he listens to Barbas' astral projection telling him how Zola is just like Gideon was.
Piper holds Leo and tells him no one else is ever going to know.
Back at the house, there are paramedics for Sheridan and she can't remember why she was even there in the first place. Paige has a potion vial, most likely to be used on Barbas.
Source: The Prophecy
The roles being auditioned for this episode are: Attendant, Fierce Demon, Jean, Paramedic Garcia, Priest, Zola.
Source: Show Fax
An enraged Leo wants to kill Barbas because he helped Gideon. Barbas tries to have Leo think that all good guys aren't who they seem to be including an Elder named Zola. The latter goes to the manor to warn the girls that Leo just tried to kill him. He tells the girls that if Leo's obsession of wanting Barbas to pay isn't stopped, the Elders will have to take care of Leo themselves and have him restart the circle of life. Piper, Leo, Baby Chris, and Phoebe attend a wedding. Barbas enrolls other demons to help him go after the baby so Leo wants revenge once again and make a fatal mistake and leave the Charmed Ones without protection. Paige learns that Magic School is closing. Inspector Sheridan and Darryl, Elise and Wyatt also appears.
Source: Spoiler Fix
The one thing that did jump out is a scene at a wedding, not for any of the sisters but a family friend. Piper, Leo and Phoebe attend the wedding with baby Chris, earlier in the episode Piper doesn't want to attend, Paige is at Magic School. Anyways, the sisters and Leo are late to the wedding and have a discussion outside the church once they arrive, which gets interupted by baby Chris crying. At this point Phoebe convinces Piper and Leo to go into the church and she'll stay outside with the crying baby. I got the feeling from this scene that Phoebe is going to be greatly involved in Chris's upringing and that maybe her sabbatical is to deal with raising Chris. Also, there was no hint of Nick Lachey's character.
Barbas is trying to make Leo believe that the other Elders are after Tiny Chris, which leads to Leo killing another Elder. Barbas mentions that a "Creature" cloaked his lair to keep Leo from tracking him. Leo wants to kill Barbus for his part in Big Chris' demise.
There's a scene with Inspector Sheridan and Darryl at the manor with a search warrant, to which Phoebe says to Darryl, "So? What's she going to find?"
Leo apparently injures Sheridan by TK-ing her across the room when she shows up with gun drawn.
As for Leo, if he doesn't stop his uncontrolable vengance against Barbas, he can possibly harm an innocent. If this does happen the Elders, in this episode the main one is named Zola, they will be forced to recycle him. This means being reborn, starting the cycle of life again.
Source: Television Without Pity