High school senior Buffy Summers (Kristy Swanson) is introduced as a stereotypical, shallow cheerleader at Hemery High School in Los Angeles. She is a carefree popular mean girl whose main concerns are shopping and spending time with her rich, snooty friends and her boyfriend, Jeffrey. While at school one day, she is approached by a man who calls himself Merrick (Donald Sutherland). He informs her that she is The Slayer, or Chosen One, destined to kill vampires, and he is a Watcher whose duty it is to guide and train her. She initially rebukes his claims, but is convinced that he is right when he is able to describe a recurring dream of hers in detail. In addition, Buffy is exhibiting uncanny abilities not known to her, including heightened agility, senses, and endurance, yet she repeatedly tries Merrick's patience with her frivolous nature and sharp-tongued remarks.
After several successful outings, Buffy is drawn into conflict with Lothos (Rutger Hauer), a local vampire king and his acolyte, Amilyn (Paul Reubens). Two young men, Oliver Pike (Luke Perry), and best friend Benny (David Arquette), who resented Buffy and her friends due to differing social circles, are out drinking when they are attacked by Amilyn. Benny is turned but Pike is saved by Merrick. As a vampire, Benny visits Pike and tries to get him to join him. Later, when Pike and his boss are discussing Benny, Pike tells him to run if he sees him. Not only this, but a studious girl from Buffy's class, Cassandra, is abducted one night by Amilyn and sacrificed to Lothos. When her body is found, the news spreads through LA and Hemery High, but her murder is met with indifference from Buffy's clique.
When Pike realizes there is something wrong with Benny and that he is no longer safe, he decides to leave town. His plan is thwarted, however, when he encounters Amilyn and his tribe of vampires. Amilyn hitches a ride on the hood of his van which crashes into a tree just before Amilyn loses an arm. Buffy and Merrick arrive to rescue him and Amilyn flees the fight to talk to Lothos. After this encounter, Buffy and Pike start a friendship, which eventually becomes romantic and Pike becomes Buffy's partner in fighting the undead.
During a basketball game, Buffy finds out that one of the players, and a friend of Jeffrey's, is a vampire. After a quick chase to a parade float storage yard, Buffy finally confronts Lothos, shortly after she and Pike take down his gang. Lothos puts Buffy in a hypnotic trance, which is broken due to Merrick's intervention. Lothos turns on Merrick and impales him with the stake he attempted to use on him. Lothos leaves, saying that Buffy is not ready. As Merrick dies, he tells Buffy to do things her own way rather than live by the rules of others and he says "remember about the music." Because of her new life, responsibilities, and heartbreak, Buffy becomes emotionally shocked and starts dropping her Slayer duties. When she arrives at school, she attempts to explain everything to her friends, but they refuse to understand her as they are more concerned with their upcoming school dance, and Buffy falls out with them as she realizes she is outgrowing their immature, selfish behavior.
At the senior dance, Buffy tries to patch things up with her friends but they turn against her, and she is dismayed to find Jeffrey has dumped her for one of her friends. However, she meets up with Pike and as they start to dance and kiss, Lothos leads the remainder of his minions to the school and attacks the students and the attending faculty. Buffy confronts the vampires outside while Pike fights the vampiric Benny. After overpowering the vampires, she confronts Lothos inside the school and kills Amilyn. Lothos hypnotizes Buffy again and when the dance music stops, she remembers Merrick's words and is ready to defend herself and fight. Lothos ignites her cross but she uses hairspray to create a makeshift flame-thrower and burns him before escaping back into the gym. Buffy sees everybody recover from the attack, but Lothos emerges again getting into a fight with Buffy, who then stakes him.
As all of the survivors leave, Buffy and Pike decide to finish their dance. The film then ends with the two of them leaving the dance on a motorcycle, and a news crew interviewing the students and the principal about the attack during the credits.
Output: What made Buffy drop temporarily her vampire slaying responsibilities?