Willow unpacks and settles back in her old room with the gang's help. As they set things up, the subject turns to Anya, and how she's eased up on the whole vengeance thing.
Little do they know Anya's responsible for the deaths of twelve frat boys -- looks like her latest vengeance spell wreaked a little more havoc than she may have intended. "What have I done?" she asks herself before trying to scrub her hands clean of blood. Thinking back, she recalls her life in...
Sjornjost, circa 880. Anya, originally called Aud, plays with -- gasp -- bunnies! She's a bit jealous that Olaf, her sweetheart, might be running around on her with a bar matron. Anya was kind and generous in those days, but according to Olaf, seemed to still have the annoying characteristic of always speaking her mind and taking things literally. Some things never change.
On the UC Sunnydale campus, Willow successfully begs her way back into classes with a professor. Over the prof's shoulder, she sees Anya stumbling out of the frat house, looking freaked. Despite Anya's claims of a new and sexually virile fraternity boyfriend, Willow knows something's up. She investigates the frat house and is horrified by the discovery of the dead boys. She hears a cry, and finds a girl sobbing in the closet mumbling, "I take it back" over and over. Apparently the girl's boyfriend had broken up with her in front of his friends, and she'd made a wish that they'd all know what it felt like to have their hearts ripped out. A demonic spider conjured up by Anya appeared and took care of the wish. The very same spider attacks Willow, but she uses magic to toss it through a window. For a moment, though, there's an eerie glimpse of Dark Willow as she fights the demon, which unnerves her.
Back in 880, the townspeople chase after a huge troll -- it's Olaf! Aud cast a little spell on him after discovering his little infidelity with the bar matron. The demon D'Hoffryn appears, impressed by Aud's magical ingenuity, and asks Aud to join his demonic family. He calls her Anyanka, and says if she'll join with him, she will realize her true self.
In Anya's apartment (current day), Hallie visits a guilt-ridden Anya. She's reeling from the deaths of the frat boys, and Hallie does her best to console her. Anya is relieved, until an extremely pissed off Willow arrives. The witch demands an explanation of the bloodshed, and though Anya declares, "They got what they deserved," she still seems unsure of herself.
Meanwhile, Buffy and Xander are on the hunt for the spider, but it finds them first. It attacks Buffy, but she fights it off and chops it with a well-aimed ax. After they return home, Willow fills them in on Anya. Xander is furious that Willow didn't tell them about Anya's evil deeds earlier, but he falters when Buffy reveals that she has to kill Anya. Xander argues against it -- he still loves his ex. But Buffy must draw the line somewhere. It's her duty as the Slayer. Xander leaves to warn Anya, and when Buffy asks Willow to help her, Will turns her down. After Buffy leaves, the witch calls on D'Hoffryn for a little chat.
Xander finds Anya at the frat house, but Buffy's right behind him. The Slayer is armed with a sword, and she uses it with force when Anya goes all demon-y. Buffy stabs Anya in the heart, but that's not enough to fell a vengeance demon. Buffy is about to finish her off when Xander intervenes, much to Anya's dismay. D'Hoffryn appears in a cloud of smoke at Willow's behest, and Anya pleads with him to take back what she did to the frat boys. She's willing to sacrifice herself. D'Hoffryn goes for the throat -- he takes back the spell and revives the boys, but ends the life of Anya's dearest friend Hallie instead. Anya is devastated, and Xander tries to offer comfort. However, the former demon needs to find out who she really is on her own, and with tears streaming down her cheeks, she walks off into the night.
Summary from Buffy.com