While patrolling the graveyard, Buffy stumbles upon Spike who wants to talk about their kiss. As Buffy explains that she doesn't care about it, she jumps on Spike to help him avoid a flying stake. Across the graveyard, a shark demon named Teeth and two vamp henchmen appear. They claim that Spike owes them 40 Siamese kittens. After a short battle, Spike disappears.
At Xander's apartment, the gang discusses bringing Buffy back from a heavenly dimension. Willow informs everyone that she can concoct a spell that will make Buffy forget she was even there. At this point, Tara gives Willow an ultimatum: She can't use magic for a week, or Tara will leave her.
The next morning, Tara and Dawn wait for Willow, who is dragging her feet getting ready. Frustrated, Tara and Dawn leave. After they depart, Willow casts a spell with a crystal and a Lethe's Bramble to make Buffy forget about being in a heavenly dimension and Tara forget about the fight.
The whole gang regroups at the Magic Box to find out more about Teeth. Giles reveals that he is returning to England indefinitely. As Buffy holds back her tears, she and the entire gang pass out.
Later that night, the Scoobs all wake up with amnesia. As they try and piece things together, Giles and Anya decide that they are engaged. Spike thinks that his name is Randy and that he is Giles' son. Buffy doesn't know her name and dubs herself "Joan". Xander and Willow think that they are a couple. Tara figures out her name and that she is a student. Dawn doesn't understand what is going on, but realizes that "Joan" is her sister.
The gang decides to go to a hospital, but they are shocked by two of Teeth's vamp henchmen waiting outside. Xander finds the trap door in the store that leads to the sewers. Suddenly, the vamps bust in. Buffy dusts one of them while the other vamp escapes. He returns with three more vamps and their leader, Teeth. Buffy decides that she and Spike will take the monsters on the run, while Anya and Giles try to break the spell. Xander and the rest go through the sewers to find a hospital.
Buffy and Spike burst from the Magic Box, temporarily eluding the vamps. Soon the bloodsuckers track them down. After throwing a punch, Spike vamps out, scaring Buffy.
Meanwhile, in the sewer, Dawn, Xander, Tara and Willow try to find their way to the hospital. To their surprise, there is another vamp hunting them down in the tunnel. Back at the Box, Giles and Anya try unsuccessfully to use magic. Mistakenly, Anya reads a spell that makes white bunnies appear.
On the streets, Buffy tells Spike that he is a vamp. Suddenly, Spike comes to the conclusion that he is a noble vampire with a soul. "A vampire with a soul?!" Buffy asks. "How lame is that?" However, she and Spike decide to stand together against the forces of darkness.
As the remaining Scoobs try to run and hide from the vampire in the sewer, Giles and Anya fight with bunnies, each other and all sorts of other crazy things at the Magic Box.
While jumping to save Tara from the vampire, Willow accidentally drops the magic crystal. After Giles successfully dispels all of the badness at the Box, he and Anya make up by embracing each other with a kiss. Xander dusts a vampire and crushes the crystal. As a result, the spell is broken.
As reality comes back into focus, Tara starts crying, knowing that everything was caused by one of Willow's spells. Stunned, Anya and Giles freak out mid-kiss and try to act casual. Back in the battle zone, Buffy and Spike finish off the vamps. Teeth, slightly entertained and frightened, lets Spike off the hook.
The hellish day concludes with a montage. To Dawn's tears, Tara packs her bags and leaves Willow. Giles returns to England.
Summary from Buffy.com