Leo is up in the attic teaching Billie the history of magic without much success – she'd rather be practicing her fighting technique. Billie accidentally taps into using her telekinesis to redirect her nunchaku, bringing the class to a sudden close.
Piper and Paige are having a morning get-together as Paige heads out for a morning date set up on the Internet, and discuss Wyatt's upcoming school play - Cinderella. Piper is unhappy with her new life and they discuss Phoebe's concern about Dex. Phoebe interrupts to announce her most recent scrying reveals her vision is correct. When Phoebe is getting Wyatt ready at school, another mother, Mandi, is in charge and comes over and gives her some advice, then mentions a pumpkin costume Piper had forgotten. Afterward Mandi destroys the costume using magical powers and it's clear she's a demon.
Paige meets with her new date and covers for her fake background – she's quickly bored by the guy's thrilling office life, then notices Dex meet with another woman and share an embrace. She goes to visit Phoebe at the office and hints at how much Phoebe knows about Dex's background, and Phoebe doesn't want to hear anything.
Piper is venting on Leo because she's behind on keeping up with her costumes, so she decides to use a spell from the Book of Shadows to play catch-up. Leo talks her out of it by pointing out it's more about her and Mandi. At Magic School, Mandi meets up with the demons running the place and reveals she's trying to gain Wyatt's trust, while having her minions clean up the place to set up somewhere comfortable for Wyatt. The demon inside Mandi hops out revealing she's possessed.
The next day Piper finishes Wyatt's costume and is clearly concerned that others think she's only Wyatt's cousin, not his real mother. Paige wants to talk about Dex's date and resolves to find out who the mystery woman is. The possessor demon deals with one of her underlings who wants answers, and she reveals she wants Wyatt for a power he has to bring back a particular demon – The Source.
Paige arranges an "accidental" meeting with the woman, Sylvia, and claims she's a friend of Dex's. Sylvia claims they were just saying hello and that they were dating months ago, but they're still getting together for break-up sex on occasion. At the school, "Mandi" reveals they're doing mice costumes now and gets some other mothers to gang up to make sure Wyatt isn't traumatized, while poking at Piper's fake status as Wyatt's cousin. Leo calls to let Piper know Billie wants to go to Magic School to get access to all the training stuff, and she vents about Mandi before saying no to Billie's plan. Leo breaks the news to Billie, who teleports them to Magic School and they spot the demons.
They hide and realize they don't have a way back unless they can find a spell, and Billie has to knock out a couple of demons. Piper gets back home to find them messing while Mandi works further on Wyatt to get him to her side and do magic for her – he starts to do so. Paige takes on the form of Sylvia and meets with Lex to come on to him, but he has no idea what she's talking about and says they haven't had sex at all. Phoebe shows up and Paige-as-Sylvia makes a quick exit.
Billie and Leo disguise themselves as demons to look for the teleport spell and spot "Mandi" and Wyatt as they arrive. The assistant demon is concerned the Source may not be happy with them but "Mandi" assures them he'll be glad to have Wyatt as his new "son." Leo finds the spell and tells Billie to leave without them. Piper arrives to find Wyatt missing with Mandi and quickly figures out Mandi is a demon. Paige gets home and Phoebe jumps her, having figured out Paige was disguised as Sylvia. Piper breaks them up to start looking for Wyatt and Billie arrives to bring them up to speed.
"Mandi" shows Wyatt how to summon the Source and he does so as Leo looks on. "Mandi" takes credit for his resummoning and reveals Wyatt's nature. The Source is skeptical but "Mandi" notes Wyatt will need a mommy. The Source approaches Wyatt but Leo intervenes and claims he was with Zankou, and Wyatt goes to him. As the Source questions Leo and "Mandi" tells the other demons to leave, the Halliwells 'port in. The Source sees through Leo's bluff but the sisters come in and force the possessor demon out of Mandi's body. Piper banishes the possessor demon, and since she summoned the Source, the Source is banished as well.
Later Billie and Paige chat and Paige acknowledges they're worried about demons at Magic School. Dex arrives to talk to Phoebe and reveal he's been in contact with Sylvia, but that he wants to be with "Julie" now. Phoebe thanks Paige, who is listening in. And at the school, Piper and Leo arrive for the school play and are happy for their "perfect moment."