Elliot Spencer and Allison Michaels discuss their upcoming wedding. Elliot's mother, Grace Spencer, joins them and asks if they've gotten a marriage license yet. Just then, a mysterious blonde appears in the driveway. The woman, Jade, reminds Mrs. Spencer that 20 years earlier, they made a pact in which Mrs. Spencer would receive great wealth and power in return for her eldest son's hand in marriage–and Jade is now here to collect. Jade gestures and Elliot collapses.
Piper takes a pregnancy test. She fears she may be carrying the child of Jeremy Burns, her ex-boyfriend who proved to be a warlock. Phoebe finds the box in the trash and has a vision of a demon child being born.
Piper prepares to cater the Spencer wedding. She is stretched thin, especially since Chef Moore, who was originally supposed to cater the wedding, is in Europe. Piper asks Phoebe for help. As Piper enters the Spencer estate, a priest, Father Trask, appears. He tries to warn Piper of Hecate, as security guards throw him out.
Prue is in the midst of cataloging a fertility icon. It's mere presence is supposed to ensure a woman conceives. Rex walks in and says the goddess is no longer available, and reminds Hannah that it was acquired for someone else. Phoebe drops into Prue's office, and tells Prue about her premonition.
Allison demands an explanation for why Elliot is suddenly due to marry Jade, but Grace only says that Jade is an old family friend and gives Allison the brushoff.
Phoebe and Piper learn of the change of bride. They go to meet her and Grace. The two are alarmed that Chef Moore won't be handling the wedding, but Piper and Phoebe reassure them. A seamstress is altering Jade's dress and sticks her with a pin, but Jade doesn't even flinch.
Allison manages to sneak into Elliot's room. Just as they start to talk, Grace, Jade and Kirsten, one of the bridesmaids, walk in and hustle her back out. Elliot begs Kirsten not to harm Allison, and a visibly, angry Jade pulls him back into the room.
Father Trask sneaks back into the estate in a delivery truck. He puts on a deliveryman's uniform and takes a large dagger with him. He finds Jade and raises the dagger, calling her Hecate. However, Jade doesn't seem to be at all alarmed. Kirsten fades in behind Father Trask. She morphs into a demon and breaks his neck. Jade has him thrown from her window.
Piper and Phoebe run into Allison, who tells them of her plight. Piper wants to help; she thinks this is something they're supposed to do as good witches.Jade tells Andy and Darryl that Trask had lunged at her with the knife, but she ducked out of the way and he flew out the window. The two cops are skeptical, as Trask had landed too far from the window. Meanwhile, Grace angrily tells Kirsten that killing Father Trask was not part of their deal. Kirsten then threatens to kill Grace if she tells anyone about what happened.
Prue wants to know if the fertility icon's male counterpart can still be catalogued, and Rex approves. He mentions the female icon was a gift for Elliot's bride. Prue says that Piper is catering that wedding, but she won't be going. Rex runs into Hannah, and confirms that Prue won't be there. However, he thinks it's too risky for them to go.
Prue is pulling an inventory tag off the male icon's "artifact", when Andy walks in with the dagger. She reads an inscription on its blade: "Nec prius absistit quoad protero prodigium", which she translates as "I shall not rest until the demon is vanquished" (though more adequate translation would be: "The demon will not rest until I have vanquished him."). She searches the Web on her laptop, and finds out about Hecate.
Piper notes that the napkins and the catering contract both mention Allison, not Jade. Phoebe tells Piper of her vision, and Piper assures her that she's not pregnant. Phoebe realizes that she had not in fact seen Piper in her vision. Prue tells what she has found out about Hecate -- and that based on her research, Jade is really Hecate in human form. Hecate comes to Earth every 200 years so she can marry the first-born son of a prominent family and use him to have a child. The child may look human, but will be pure demon. The dagger is actually a poingnard, which is the only thing that can destroy her.
The sisters spy on Jade's bachelorette party. A "pizza deliveryman" comes in, and starts taking off his clothes. Jade and the bridesmaids approach -- and then Jade sinks her claws into the stripper, killing him.
The next day, the sisters make plans to crash the wedding. Allison can break Hecate's spell with a declaration of true love, sealed with a kiss.
Prue calls Allison to the manor and convinces her to crash the wedding. Phoebe and Piper talk to Mrs. Spencer, who seems to agree to stop the wedding. She tells Piper and Phoebe to meet her in the wine cellar. Piper and Phoebe slip into the cellar, but two of the bridesmaids follow them. Piper tries, unsuccessfully, to freeze the bridesmaids, but she's too far away. Piper and Phoebe run and hide. Prue and Allison reach the Spencer estate; Prue calls Piper's cell phone and Piper tells her where she is. Piper, at last, freezes the bridesmaids as Prue enters the cellar and flings them into a wall. The sisters and Allison interrupt the wedding. Jade raises a windstorm and grabs Elliot, while the guests scatter.
The sisters find Jade and Elliot in an upstairs room, just as Jade is morphing into her demon form and about to be impregnated by Elliot. The bridesmaids, also in demon form, rush in after them. Prue cannot find the dagger – it's on the floor next to Elliot. Elliot raises the dagger, and Prue draws Jade and the bridesmaids into it. The wedding proceeds with Allison. Andy stops by and Prue gives him the dagger.