About 'Prophecy Girl' :
Xander is practicing lines on Willow in the Bronze, preparing how best to ask Buffy to the prom. Cordelia is in a car making out with Kevin, as Buffy slays a vampire nearby. An earthquake is felt all over town, and the Master revels in it.
The next morning, Buffy is meeting Giles in the library, where no significant damage was sustained in the earthquake. Buffy explains that the vampires are rising in number and getting braver, but Giles is distracted by his thoughts. After biology class, Willow finds an excuse to leave, leaving Xander alone to ask Buffy to the prom. Buffy gives him the "let's just be friends" routine. Xander takes the rejection badly, and walks off to wallow in his misery.
Meanwhile, Miss Calendar interrupts Giles' study in the library, telling him that she sees apocalyptic portents and demands to know what is happening. She tells him Brother Luka, a monk in Cortona, is e-mailing her about the Anointed One. Giles asks her to get more information about this, promising he will explain everything later. In the school hall, Kevin and Willow promise to help Cordelia set everything up in the Bronze for the dance. Willow sees Xander wallowing in his misery and offers sympathy. When Xander asks her to the dance, she refuses to be his second choice.
That evening, as Buffy enters the library, she hears Giles telling Angel that the prophecies say that she will face the Master and die. A shocked Buffy yells that she is quitting, leaving the cross Angel gave her on the table. She goes back home and tries to convince her mother to go away for the weekend. Instead, Joyce gives her a stunning white prom dress, and after she tells her about when she met Buffy's father, encourages her to go to the dance.
The next day at school, Cordelia and Willow find the members of the audio video club, including Kevin, slaughtered by vampires, as "Three Little Pigs" cartoons play. Having heard the news, a sympathetic Buffy shows up at Willow's, all decked out in her prom dress. Willow is shell-shocked; even though she has faced vampires and death before, until this it has never been quite so personal. Buffy heads back to the library, where Giles has explained to Miss Calendar that Buffy is the Slayer. Buffy reinstates herself as the Slayer, knocks Giles out when he tries to stop her and goes to face the Master. Outside of school, Colin the Anointed leads her by the hand to the Master's lair.
Willow and Xander show up at the library, where they discover that Buffy has gone off to see the Master. Xander leaves, only to show up at Angel's apartment, where he forces Angel to lead him to the Master's lair. Xander and Angel approach the lair, as the Master and Buffy fight and taunt each other. The Master tells Buffy that it is her blood which will free him, drinks from her and leaves her to drown in a shallow pool. At the library, Willow and Ms. Calendar decide that the Hellmouth is underneath the Bronze, and leave. However, as they leave, they see an army of vampires approaching the library. Cordelia rescues them in her car, and drives the car straight into the school. Xander and Angel reach Buffy, and Xander performs CPR (as Angel couldn't do it himself, since vampires don't breathe). When Buffy regains consciousness, she heads to the surface to kill the Master. Cordelia, Willow, Giles and Jenny fight off vampires trying to enter the library, and just as Giles realizes that the Hellmouth is directly underneath the library, a tentacled creature rises through the floor. Buffy throws the Master into the library, where he is impaled on a jutting piece of wood and his soft tissues disintegrate, leaving only his skeleton and the world turns back to normal. The stunned friends stare at each other wondering what to do now. "We saved the world. I say we party," suggests the resurrected Slayer. They then head off.
Info from the Buffy Wiki.