When Willow Rosenberg, Tara McClay, Xander Harris and Anya Jenkins performed the powerful dark spell to resurrect the deceased slayer Buffy Summers, little did they know that their actions would start a chain of events that would change the history of the world, and forever change the destiny of the slayer. Sensing that the mystical energies surrounding the slayer line were weak, a primal force known as the First Evil began to execute its plan to end the slayer forever. Before long, potential slayers, girls training to one day be the next slayer, along with their watchers, were turning up dead, murdered in cold blood by the First's minions, the Bringers.

The Watcher's Council, aware of the First's attacks, began to assemble a counter-strike, deciding for whatever reason, not to inform Buffy or her friends of the coming danger. Before the Council could prepare its counter attack however, an agent of the First was sent to destroy the Council HQ in London, blowing up the records and all of the senior staff of the Council itself, leaving the once great Council of Watchers in ruins, and its operatives around the world imobilised.

Amid the death and destruction, Buffy's watcher, Rupert Giles, assembled his own plan, after finding one of his colleagues seriously injured by Bringers. Stealing several books and records from the Council before its destruction, and finding a handful of living potential slayers along the way, Giles travelled to Sunnydale, to warn the slayer of the pending apocalypse, and to formulate a defense against the First. Upon his arrival in Sunnydale, Giles informs the gang that potential slayers from all over the world are heading to the hellmouth for protection.

Hunting for the First's lair on Giles' first night back in Sunnydale, Buffy stumbles across the lair by accident, and comes face to face with the First's powerful minion, the Turok-Han. After a series of encounters with the ancient vampire, Buffy is left beaten and damaged, leaving the gang to wonder whether she'll be able to fight the coming darkness. Buffy recovers quickly however, and declares all-out war on the First, as more and more potentials begin to show up in Sunnydale.

After defeating the Turok-Han, Buffy sets about training the young girls who are now entrusting her with their lives. Meanwhile, she discovers the true dark origins of the slayer power, and has a horrific vision of what is to come in the future.

After various encounters with agents of the First (leading to many injuries and deaths), and after Faith's less than welcome return to Sunnydale, Buffy discovers an ancient scythe forged especially for the slayer, that was lost to the slayer line centuries before. From this symbol of power, Buffy begins to formulate her final battle against the First Evil, as Faith leads the potential slayers into a disasterous situation.

Underneath the high school, the potentials who survived the bomb blast laid in wait for them, gather together to get the unconscious Faith out of harm's way. That is until they discover the blast seems to have released several Turok-Han from the hellmouth. They potentials prepare to fight, but are only saved when Buffy shows up just in time, using the scythe to slay the ancient vampires with ease.

As the potentials and Faith recover from their attack, Buffy introduces her plan to take out the First. As the Summers' house is turned into a medic center for the wounded, the gang start preparing for the final battle.

At Sunnydale High, Buffy, Faith and Spike lead the potential slayers into the hellmouth, where the epic battle between the Turok-Han and the champions of good begins. As planned, Willow uses the scythe's power to activate all the potential slayers, giving them equal power to Buffy and Faith. No longer only potential, the slayers stand side by side to defeat the evil that has terrorised them for so long...

Thanks to a little assistance from Spike's amulet, the Turok-Han are wiped out, and the slayers and the Scooby Gang struggle to escape the hellmouth and the high school, as Sunnydale begins to sink into the ground. As Buffy watches Spike save the world, the survivors of the battle climb into an old school bus and begin to drive to safety, as Sunnydale collapses all around them. As Spike dies, Buffy leaps from building to building to keep up with the school bus, before finally leaping to safety on top of the bus.

With Sunnydale now nothing more than a hole in the ground, the survivors gather around the city limit, and look into the place that had caused them all so much grief. Willow: "The First is scrunched, so... what do you think we should do, Buffy?"