Buffy and Angel kiss tenderly, then pull back to stare into each other's eyes. He came to help knowing the First was at work, but his explanation is interrupted by a whack on the head from a not-quite-dead Caleb. The preacher attacks, black blood running from his eyes and mouth, and he and Buff have at it. Buffy finally does him in with a swing to a rather important part of his anatomy, dragging the scythe up and slicing him in half. That seems to do the trick.
Angel has brought with him an amulet with cleansing powers, and though he's not exactly sure how it works, it must be worn by one who will be Buffy's champion. Angel wants to stay and fight by her side, but she asks him to go back to L.A. She says it's so he can form a second front in case she fails, but Angel suspects that Spike is the reason. She denies that Spike is her "boyfriend," but admits, "He's in my heart." Buffy can't see the future or what it will bring, though sometimes she does imagine being with Angel again down the line. Angel is willing to wait, and walks off into the darkness.
When Buffy gets home, Dawn gives her a kick in the shins for trying to get her out of town. Buffy finds Spike downstairs in the basement, sulking. He says he saw her kissing Angel, and Buffy doesn't react well to the jealous Vamp stuff going around. Spike holds out a hand for the amulet, knowing it's meant for him. He's disappointed when she explains it must go to her champion, until she hands it over. When Buffy explains that Faith is still sleeping in her room, Spike shelves his pride and asks her to stay. She does.
Buffy can't sleep, though, and soon is confronted by the First as Caleb. He gives the requisite "I'm going to rule the world" speech again, but Buffy's not afraid. She is shaken, however, when the First morphs into an exact replica of her, like she's looking in a mirror. The First tells Buffy she lives her life alone and will die that way. When it disappears, Buffy comes to a realization: "We're gonna win."
She has a new plan that requires some serious Willow mojo. Giles loves the idea, but Willow's nervous. She's afraid she won't have the control to follow through with the spell she'll have to perform, but Kennedy promises to buoy her up. That night, it appears Giles and Xander are mapping out their positions for tomorrow, until it's revealed they are playing a handwritten wizarding game with a red-caped Andrew, Amanda and a snoring Anya.
The gang--the whole gang this time--heads for the school in the morning, ready to kill anything that moves. The Potentials start off, leaving the Scoobies one last moment to come together. Dawn won't say goodbye to her sister, walking away without saying anything. Buffy, Willow, Xander and Giles discuss future plans for after the fight, including checking out the new Agnes B. store at the mall. Giles shakes his head at the three of them as they stride down the hall, splitting off one by one till Buffy's on her own.
The Slayer arrives at the Seal, surrounded by Potentials. One by one, they slice their hands to drip blood on the Seal until it opens. "We're going to Hell," Faith announces, and the girls descend into the ground, while upstairs Willow (with Kennedy's help) prepares her spell.
Spike, Faith, Buffy and the girls look out over a vast canyon filled with Ubervamps, and they hope Willow can work her mojo fast. The bad guys spot them and rush in, and just in time, Willow's spell takes effect. Energy pours through Willow, and suddenly the girls in the cavern, as well as girls around the world, are imbued with the strength of a Slayer. Will has harnessed the ancient energy of the scythe and sends it out so all the girls with the ability to be a Slayer fulfill their potential. The former Slayerettes wield their powers instantly, lashing into the Ubervamps with relish. Willow's hair goes white for a moment, then reverts to red once the power leaves her. She sends a newly Slayerized Kennedy out to carry the scythe to Buffy.
Meanwhile, there's a MASSIVE FIGHT going on underground, the Slayers kicking butt and not bothering to take names. Some of the Vamps escape upstairs, but the rest of the gang is there to defend their ground. Giles holds his own, but Wood takes a knife to the gut. The Bringers attack Andrew and Anya, and somehow, Andrew manages to survive while Anya is taken down. When Buffy is yelling orders to the girls, a Vamp stabs her through with a sword. As she falls, Faith rushes to her side, and Buffy whispers, "Hold the line" while handing Faith the scythe.
The First taunts Buffy about her mortal wound, but it only irritates Buffy, who somehow stands up to fight again. The First disappears, and Buffy retakes the scythe and goes to town on the Vamps. Spike stumbles back against the wall of the cavern, feeling the amulet take effect. Something shoots up out of it, blasting through the roof, showering the Vamp in a circle of bright sunlight. The light shoots through the amulet and vaporizes all the Ubervamps one after the other, eventually beginning to destroy the cavern.
Everyone runs. Xander calls for Anya, unable to see her dead body in the debris, and he's forced to leave her behind. Buffy stays with Spike until the last second, holding his hand as it catches fire. He has to do this; he can feel it in his soul. "I love you," she tells him, and he replies, "No you don't, but thanks for saying it." He sends her away, and as he disintegrates into the light, the school crumbles into the Hellmouth and starts to take the rest of the town with it.
Buffy races the ground as it falls in, chasing the school bus hauling everyone away. She leaps from a building to land on the bus roof, hanging on tightly as the bus streaks for the highway. Finally, they make it far enough away to stop and look back at the giant canyon that used to be their town. When Giles wonders what destroyed the Hellmouth, Buffy answers that Spike's the one. Andrew explains to Xander how Anya died saving his life, and that doesn't surprise Xander. Wood's badly injured, but he'll be okay.
Giles, Dawn, Willow, Faith, Xander and Buffy look out on what was once Sunnydale. They saved the world and changed it, and they'll need to find the new Slayers. Buffy is no longer the only Chosen, no longer alone. Dawn asks, "What are we gonna do now?" With the sun glinting in her eyes, Buffy smiles.
Summary from Buffy.com