Buffy's resurrection caused an instability which allows The First Evil, a spiritual entity that Buffy encountered before, to begin tipping the balance between good and evil. It has inactive Potential Slayers hunted and killed by Caleb, a sinister and misogynistic preacher turned serial killer who heads a cult called Bringers, who worship The First as a god. Inside the Hellmouth it raises an army of Turok-Han, an ancient and powerful sub species of vampire.

Willow resurrects Buffy with a powerful spell. Although her friends believe that they have taken her out of Hell, Buffy had actually been in Heaven since her death (a fact that is later revealed to her friends). She is therefore traumatized by her resurrection and this causes her to fall into a deep depression. Meanwhile Giles returns to England after realizing that Buffy has become too reliant on him, while Buffy takes up a fast-food job for money and develops a secret, mutually abusive relationship with Spike.

Dawn appears in Sunnydale as a younger sister of Buffy. No one finds this strange, but it is soon revealed that the teenager is a mystical energy called The Key that was transformed by a group of monks, using Buffy's essence, into human form. False memories were implanted in all those concerned to protect the fourteen-year-old from Glory, an exiled God from a demon dimension who wants to leave the human body in which she is trapped (Ben the hospital intern) for her home universe.

Buffy and Willow enroll at UC Sunnydale while Xander joins the workforce. The vampire Spike, having left Drusilla, returns to Sunnydale and is abducted by The Initiative, a top-secret military installation based beneath the UC Sunnydale campus, led by Maggie Walsh. They implant a microchip in his head which prevents him from harming humans. He reluctantly helps the Scooby Gang throughout the season and eventually begins to fight on their side after learning that he can harm other demons. But Buffy and her friends don't trust him except Willow who opts to give him a chance to redeem himself, which they eventually do.

After attempting to start a new life in Los Angeles, Buffy Summers returns to Sunnydale, and is reunited with her friends and her mother. She is no longer a criminal suspect; but Principal Snyder, who took a vindictive pleasure in expelling Buffy, refuses to reinstate her until he is told down by Giles. Angel is resurrected mysteriously by the unseen Powers That Be. While Buffy is happy to have Angel back, he seems to have lost much of his sanity in Hell. Buffy helps Angel recover but, having seen Angel's demonic side, Buffy's friends distrust him until he saves them from a monster.

Buffy Summers has just moved to Sunnydale after burning down her old school's gym and hopes to escape her Slayer duties. Her plans are complicated by Rupert Giles, her new Watcher, who reminds her of the inescapable presence of evil. Sunnydale High is built atop a Hellmouth, a portal to demon dimensions that attracts supernatural phenomena to the area. Buffy meets two schoolmates, Xander Harris and Willow Rosenberg, who help her fight evil through the series. She also gets a love interest in the form of Angel, a vampire who has a soul. They soon become known as the "Scoobies". Together they must prevent The Master, an ancient and especially threatening vampire, from opening the Hellmouth and taking over Sunnydale.