Seventeen-year-old Isabella "Bella" Swan moves to Forks, a small town near the Washington coast, to live with her father, Charlie, after her mother is remarried to a minor league baseball player. She is quickly befriended by many students at her new high school, but she is intrigued by the mysterious and aloof Cullen siblings. Bella sits next to Edward Cullen in biology class on her first day of school; he appears to be disgusted by her, much to Bella's confusion. A few days later, Bella is nearly struck by a van in the school parking lot. Edward inexplicably moves from several feet away and stops the vehicle with his hand without any harm to himself or Bella. He later refuses to explain this act to Bella and warns her against befriending him.

After much research, Bella eventually discovers that Edward is a vampire, though he only consumes animal blood. The pair fall in love and Edward introduces Bella to his vampire family, Carlisle, Esme, Alice, Jasper, Emmett, and Rosalie. Soon after, three nomadic vampires—James, Victoria, and Laurent—arrive. James, a tracker vampire, is intrigued by Edward's protectiveness over a human and wants to hunt Bella for sport. Edward and his family risk their lives to protect her, but James tracks Bella to Phoenix where she is hiding and lures her into a trap by claiming he is holding her mother hostage. James attacks Bella and bites her wrist, but Edward, along with the other Cullen family members, arrives before he can kill her. James is destroyed, and Edward sucks James's venom from Bella's wrist, preventing her from becoming a vampire. A severely injured Bella is taken to a hospital. Upon returning to Forks, Bella and Edward attend their school prom. While there, Bella expresses her desire to become a vampire, which Edward refuses to grant. The film ends with Victoria secretly watching the pair dancing, plotting revenge for her lover James's death.