After defeating The Master, Buffy returns from summer vacation, only her friends find a cold and distant demeanor has replaced her usual cheery self.
Two students are digging up the bodies of teenage girls in order to create the perfect woman, with Cordelia's head as the last part to be sought.
When a vampire named Spike arrives in Sunnydale to restore his ailing love, Drusilla, with the aid of the Hellmouth, Buffy must fend off his gang while keeping everyone safe during parent-teacher night.
Buffy hosts a foreign exchange student named Ampata, who she believes to be a male, but is surprised to learn he is actually a female whose identity has been usurped by an ancient Incan mummy princess. She needs bodies to live, and when Xander asks Ampata to a school dance, he becomes her next potential victim. Willow pines for Xander, but all the while, a student named Oz is becoming smitten with her.
Buffy accepts an invitation to join Cordelia at a fraternity party where, after being drugged, both soon become human sacrifices for a snake-like demon.
Buffy, Xander, and Willow are forced by Principal Snyder to take some kids trick-or-treating on Halloween, but after going to a new costume store to get their costumes, they take on the identity of the costumes when the malicious store owner puts a spell on them.
An old friend of Buffy's comes to town claiming to have been transferred to Sunnydale, only in reality he is in line with a vampire worshipping group, and the gang soon learns that he has offered Buffy to Spike in trade for a chance at vampire immortality.
When an old friend of Giles' pays him a visit, he reveals Giles' wild teenage days through the story of the demon the two unleashed and the news of its return. The demon is after the last two survivors, Giles and Ethan Rayne. The demon, however, has arrived and possessed Jenny Calender.
Buffy resigns herself to a future as a slayer, as Spike to tries to keep her away while restoring Drusilla's power. A mysterious vampire slayer named Kendra preys on Angel and locks him in a cage before going after Buffy.
Giles confirms Kendra's position as a slayer, recruited following Buffy's minutes-long death, and the two slayers clash over differing styles. An assassin has Cordelia and Xander trapped in a basement, while Oz and Willow are interruped by another assassin. When the assassin, disguised as an officer, shoots Buffy, Kendra comes to Buffy's aid. The gang then sets out to rescue Angel, now in Spike's captive.
Buffy is suspicious of her mother's new boyfriend, Ted, who seems to have captivated everybody around him.
Buffy's health class is given the task of playing the role of parents to eggs, only the eggs hatch and unleash parasitic insect creatures upon everyone. At the same time, Buffy is targeted by two cowboy vampires, and her relationship with Angel escalates.
Drusilla tries to revive an ancient demon known as The Judge, capable of bringing about armageddon by reassembling its parts. After Buffy intercepts the demon's arm, Jenny Calender convinces Angel to carry it far away, but before he can leave Sunnydale, he and Buffy are ambushed by Spike, Drusilla, and subsequently, the reassembled demon.
After making love with Buffy, Angel has once again become Angelus, and reteams with Spike and Drusilla to destroy Buffy, starting by targeting her friends. The three then set out to unleash The Judge.
Buffy and the gang track what is believed to be a werewolf loose in the woods while avoiding a preying werewolf hunter. As Willow attempts to get closer with Oz, she is unaware that he is the werewolf.
Xander employs Amy's help to put a spell over Cordelia which will make her interested in him again, only the spell ends up attracting every other woman except Cordelia.
Angelus continues to haunt Buffy by leaving gifts in her bed during the night. Meanwhile, Jenny Calender causes serious harm when she tries to translate the Gypsy curse that can free Angel's human soul.
Buffy enters the hospital with a fever and meets a boy with a similar illness who claims that a monster, possibly death, is killing the children in the hospital.
Buffy suffers guilt over Angel's transformation. Meanwhile, Sunnydale High is being haunted by the tortured ghost of a student who killed himself after killing his school sweetheart.
After various members of Sunnydale's swim team are mysteriously found skinned alive, Buffy and the gang protect the remaining members from the coach's genetically-altered players-turned-fish monsters.
As Angelus prepares to unleash Acathla, a demon that will drag Earth into the demon dimension, his origins in the 18th century are revealed. Willow and Buffy determine the spell needed to bring back Angel's soul, just as Kendra returns to Sunnyale bearing the sword that has been blessed by a knight, Acathla's first slayer.
Buffy is arrested for murder following Drusilla's attack which saw Kendra dead and Giles abducted. She is expelled from school and a fight between her and her mother ensues when she reveals she is the slayer.