Victoria, set on destroying Bella Swan, is out creating an army of newborns, hungry premature vampires under the unruly control of Riley Biers. These newborns are extremely messy about their feeding needs, much to the growing dismay of the living locals in Seattle and the Cullen vampire clan. Back in Forks, Edward Cullen and Bella discuss the complications of becoming an immortal vampire. With her dreaded 19th birthday looming, Bella will soon be two years older than Edward, and therefore, she wants to be changed. But because of the human events that she would be missing, Edward refuses to change her immediately.
Bella makes the effort to keep in touch with Jacob Black, but Jacob will not return her calls. Charlie Swan urges Bella to do this, allowing Bella the freedom in return for her company with Jacob. Charlie is covering the disappearance of Riley Biers, who is from Forks himself. Edward suspects his disappearance to be the cause of newborn vampires. Furthering his suspicions is the intrusion of Riley in Bella's room.
Although Edward fears for her safety, Bella insists that Jacob and the rest of the werewolf pack would never harm her, but Edward is still not convinced. Bella escapes to La Push to see Jacob, and arrives afterwards at her house unharmed. During one of these trips, Jacob confesses that he loves Bella and forcibly kisses her. Bella punches him which sprains her hand. When Edward finds out, he threatens to break Jacob's jaw if he ever kisses Bella without her consent again.
A few days later Bella tries to get Edward to make love to her before turning her into a vampire. Edward initially refuses, explaining to Bella that he could very easily kill her. Eventually, upon realizing how much it means to Bella, he says that he is willing to try in the future as long as they are married first. Despite having an aversion to marriage, Bella realizes that spending eternity with Edward is more important to her than anything else and accepts his proposal.
Bella and the Cullens realize that the murders in Seattle are being committed by Victoria and an "army" of newborn vampires that she has created. The Cullen family join forces with the La Push werewolf pack in order to combat this threat. As everyone else prepares for battle, Edward and Bella camp up in the mountains, where they are later joined by Jacob and Seth Clearwater, a young member of the werewolf pack, to wait out the fight. Bella, as a delicate human, starts to freeze in the harsh weather of the mountain. Jacob warms up Bella with his abnormal body heat, much to Edward's horror. During the night, Bella overhears a conversation between Edward and Jacob, in which they temporarily forget about their hatred towards each other.
In the morning, Jacob overhears Edward and Bella discussing their engagement and becomes very upset. He runs off, which causes Bella to run after him. He threatens to join the fight and get himself killed because he feels that Bella doesn't love him. When Bella begs him not to, Jacob insists that he will unless she gives him a proper reason not to. Furious, she asks Jacob to kiss her, and while doing so, she realizes that she is in love with him as well. Edward finds out about this, but isn't angry, but Bella realizes that she loves Edward more than Jacob.
Victoria eventually finds Bella's hiding spot, and Edward kills her while Seth kills her partner Riley. The Cullens and the Quileute werewolves, meanwhile, destroy her "army", though Jacob is injured when saving Leah Clearwater from a newborn. Several members of the Volturi arrive to destroy Victoria's army, and end up only killing the one newborn who surrendered. They are also told that while Bella hasn't become a vampire yet, the date for her transformation has been set.
Bella visits Jacob in his home to tell him that she has chosen to be with Edward. Heartbroken by her choice, Jacob reluctantly agrees to stop trying to come between her and Edward. Bella and Edward go to their meadow, where Edward says that they can make love before marrying if she wants to, but Bella has decided to do things his way: marriage, making love, and then becoming a vampire. Bella explains to Edward that it wasn't a choice between him and Jacob, but between who she should be and who she is. They then decide they need to tell Charlie about their engagement.