After the climactic battle on the roof of Faith's apartment building, Buffy stands alone with the knife that may have killed Faith. As the reality of not being able to use Faith's blood as a cure for Angel sets in, Buffy has a moment of painfully quiet introspection, then leaves, having made her decision internally. Just as Buffy descends the escape ladder, the Mayor and one of his goons search the apartment looking for Faith. The apartment is in a shambles, and although the Mayor tries to convince himself that Faith will prevail in the fight, his fear is written all over his face.

Back at the library, Xander and Giles research how to defeat the Mayor in demon form when Cordelia barges in demanding an explanation of why Wesley has decided to leave the country. After Giles explains that Wesley is no longer Buffy's watcher, Xander manages to convince Cordy to join in the fight against the Mayor.

Meanwhile, Willow cares for Angel back at his hideout, but things don't look so good for Angel. When he wakes up from a troubled sleep, he mistakes Willow for Buffy. When the real Buffy shows up, she asks Willow and Oz to leave so that she can be alone with Angel. When they leave, she explains to Angel that the only way for him to survive is to drink her blood. Angel emphatically resists, but after Buffy physically induces his vampire side to come out, he sinks his fangs into her neck and drains her near to death. When Angel comes to and realizes what he has done, he rushes Buffy to the hospital and demands that the doctors treat her immediately.

In the next room, the Mayor grieves over Faith, who lies in a coma. When a doctor comes in announcing another girl with 'severe blood loss' in the other room, he puts two and two together. He walks very calmly over to Buffy and tries to suffocate her, but Angel comes to the rescue. The Mayor warns Angel that at Graduation he will do much worse to Buffy, then storms out. Just as the Mayor exits, Giles, Xander, Oz and Willow meet Angel in the hall. Seeing that Angel's health has been restored, they question Buffy's condition and Angel's sudden recovery, and soon learn that Buffy's blood was the cure for Angel's ailments. While both Giles and Xander both strongly disapprove of Angel's actions, they know they must focus on the Ascension.

In a strange and surreal dream, Faith is alive and well, and gives Buffy some valuable advice: 'human weakness' is the key to defeating the Mayor. Questioning whether Faith's mind or her own mind is creating this fantasy, she drifts out of her sleep and wakes up in the hospital. She wanders over to Faith's bed and gives her an apologetic kiss, then meets the gang in the waiting room. Startled to see her up so soon, they are even more startled when she says that she is 'ready for war.'

At the library, Buffy goes over her plan with Giles, Angel, Xander, Willow, Oz and Cordelia. Wesley unexpectedly walks in, and before Buffy and the gang can ostracize him, he explains that he has not come back representing the council; he is back to help. Meanwhile, the Mayor plans his assault with his vampire goons. The vamps are told to hold the people in the area so that the Mayor can feed on them once the ascension is complete.

Back at the school, the gang goes to work rounding up students to help with the battle. Willow grabs Percy and Xander rounds up Harmony while Wesley and Cordelia share a hilariously awkward romantic good-bye in the library. In another sort of good-bye, Angel tells Buffy that if they survive the Ascension, he will not say good-bye, he will simply leave.

The big day finally arrives, and the students file in wearing their crimson caps and gowns. Anxiety and fear paint the faces of Buffy and the gang while Principal Snyder gives his usual condescending banter, then introduces Mayor Wilkins as the honored guest speaker. The Mayor begins his speech about graduation, ascension and change, but before he can finish, the ascension begins.

The moon eclipses the sun, bringing darkness over the ceremony. And before a stunned crowd, the Mayor morphs into a giant, twenty-foot dinosaur with a vicious set of teeth and a ravenous appetite. But amid the ensuing chaos, the student body is ready. Led by Buffy and a courageous Xander, the students rip off their gowns to reveal an arsenal of weapons. They bombard the demon and his vampire minions with flame-throwers, rifles, arrows, spears and swoads. In the melee, the demon dips down and grabs Principal Snyder between his jaws, and devours him. Buffy sees her chance, and orders the class to retreat. Now one on one with the Mayor, she taunts him with the knife that pierced Faith, and leads him on a chase through the high school. The chase ends in the library, which is rigged with explosives. All the Mayor can say is "Oh, gosh!" as he and the halls of Sunnydale High are blown back into hell.

In the aftermath, Giles congratulates Buffy on the victory, and presents her diploma that he pulled from the wreckage. As Giles leaves to check on the injured Wesley, Buffy spots Angel standing at a distance. They exchange a long, painful look, but before Buffy can approach Angel to say good-bye, he walks away and disappears into the smoky haze. Later that night, Buffy, Xander, Willow, Oz and Cordelia take a moment to reflect on the fact that they have not only survived the battle, but they have survived high school.