On Isabella "Bella" Swan's 18th birthday, Edward Cullen, the vampire she loves, and his family throw her a birthday party. While unwrapping a gift, she gets a paper cut, which causes Edward's adopted brother, Jasper, to be overwhelmed by her blood's scent and attempt to kill Bella. To protect her, Edward decides to end their relationship, and the Cullens move away from Forks. This leaves Bella very heart-broken and depressed.
In the months that follow, Bella learns that thrill-seeking activities, such as motorcycle riding, allow her to "hear" Edward's voice in her head. She also seeks comfort in her deepening friendship with Jacob Black, a cheerful companion who eases her pain over losing Edward. Bella later discovers that Jacob and other tribe members are werewolves. Jacob and his pack protect Bella from the vampire Laurent and also Victoria, who seeks revenge for her dead mate, James, whom the Cullens killed in Twilight.
Meanwhile, a series of miscommunications leads Edward to believe that Bella has killed herself. Distraught over her supposed suicide, Edward flees to Volterra, Italy to provoke the Volturi, vampire royalty who are capable of killing him. Alice and Bella rush to Italy to save Edward, arriving just in time to stop him. Before leaving Italy, the Volturi tell Edward that Bella, a human who knows that vampires exist, must either be killed or transformed into a vampire. When they return to Forks, Edward tells Bella that he has always loved her and only left Forks to protect her. She forgives him, and the Cullens vote in favor of Bella being transformed into a vampire, to Edward's dismay. However, Jacob reminds Edward about an important piece in the treaty; if the Cullens bite a human, the treaty is over.