Isabella “Bella” Marie Swan is thrown an eighteenth birthday party by Alice and Edward Cullen, the vampire she loves, and the rest of their vampire family. While unwrapping a gift, the paper cuts Bella’s finger. Jasper, the newest member of the ‘family’ to attempt a non-human diet, leaps for Bella, overwhelmed by the scent of blood. Edward and his family protect Bella, but the realization of the danger Bella faces due to her proximity to vampires terrifies him. Edward reveals that he believes vampires are soulless creatures who will not experience an afterlife. Edward constantly struggles with his relationship with Bella because he does not want to turn Bella into a damned creature. Edward convinces Bella that he doesn’t want her anymore, and he and his family depart from Forks in an attempt to keep her safe.
Four months pass and Bella has become a “zombie,” existing but not really living. Trying to please her father, Charlie, Bella goes to a movie with her friend Jessica. When Bella spots a group of men in an alleyway, she remembers a time when Edward save her before, and decides to approach the men. Bella then hears Edward’s voice in her head, warning her to stay away from them. Believing she may be on the verge of insanity, she concludes her subconscious mind is helping her believe that Edward cares whether she lives or dies. Thinking that the delusions are triggered by recklessness or being in a dangerous situation, she seeks other ways to trigger Edward’s voice.
Jacob Black, Bella’s friend from the nearby reservation, returns in New Moon. Bella finds two motorcycles on the side of the road and decides that they are the perfect way to hear Edward’s voice. However, they need work and she remembers that Jacob has some mechanical skills. Jacob agrees to fix them and teach Bella how to ride. When Bella rides, Edward’s voice scolds her for being “reckless and childish and idiotic.” Jacob and Bella become very close friends, with Bella relying on his warmth and friendship in order to heal from Edward’s leaving. Jacob is romantically interested in Bella, even though she makes it clear that she wants nothing more than friendship with him.
Jacob suddenly becomes very ill and fevered, but Bella faces firm resistance when she tries to contact him. Finally, Bella contacts him, only to learn that Jacob has become a follower of Sam Uley. Anxious without Jacob in her life, Bella fears she may slip back into her “zombie phase.” Desperate, she returns to Edward’s meadow in an attempt to get close to a past memory. There, she runs into the vampire Laurent, who tries to attack her. When a pack of giant wolves appear and scare off Laurent, Bella escapes.
Bella confronts Jacob, who is forbidden to explain anything to her. However, he tells her that she already knows because he told her the first night they met. Bella eventually recalls a story about werewolves and vampires and realizes that Jacob, and the rest of Sam Uley’s gang, are werewolves.
Bella’s life becomes even more difficult when Victoria arrives in Forks. Victoria seeks to avenge her mate, the vicious tracker vampire James the Cullens destroyed in Twilight. Rather than kill Edward, Victoria sees killing Edward’s “mate” as a fair trade, not realizing that Edward and his family have left Forks. It is up to Jacob and his werewolf pack to protect Bella from Victoria’s revenge. Bella spends most of her time wandering around alone since Jacob is often away with the pack searching for any sign of Victoria. She soon gets frustrated, desperate to hear Edward’s voice. Although she had planned to try cliff diving with Jacob, she cannot wait, and jumps alone. The weather is tumultuous, and the current pulls Bella under. She hears Edward’s voice pleading with her to try to fight the water, but soon she is too fatigued and resigns herself to death. Her last thoughts are “Goodbye, I love you,” before Jacob saves her life.
Afterward Bella and Jacob learn that Harry Clearwater, a friend of their fathers, has passed away. Jacob then takes Bella home, where she finds Alice waiting for her. Bella rejoices in Alice returning but soon realizes that it is only temporary. Using her gift of seeing visions of the future, Alice “saw” Bella jump off the cliff and thought that she was committing suicide. She did not see Jacob save her because, as she later finds out, she cannot see werewolves in her visions.
During Alice’s stay, Jacob is angry that Bella chose the “bloodsucker” over him. During Bella and Jacob’s argument, Edward, posing as Carlisle, calls Bella’s house. When Edward asks for Charlie, Jacob, who answered the phone, informs him that Charlie is “at the funeral.” Although Jacob means Harry Clearwater’s funeral, Edward mistakenly believes that Bella has died. Not wanting to live in a world without Bella, Edward travels to Volterra, Italy to anger the Volturi, a “royal” vampire family, into killing him by exposing the existence of vampires.
Bella and Alice rush to Italy and save Edward just in time. The three of them meet with Aro, a Volturi leader who can read minds through touch. Aro provides them with an ultimatum: either, Bella, as a human who knows of the existence of vampires, must die, or be turned into a vampire. Although Edward rejects both options, Alice shows Aro that Bella will become a vampire and the trio are released.
Bella and the Cullen family all return to Forks. Edward confesses to Bella that he left in an attempt to protect her. Bella desperately wants to become a vampire so she can remain with Edward, but Edward refuses. Bella then asks the Cullens to vote on whether they feel Bella should be changed into a vampire. All but Rosalie and Edward agree that she should be changed. Edward, who abhors the idea of Bella becoming a vampire, convinces Carlisle to wait until after graduation to change Bella.