Bella Swan (KRISTEN STEWART) still lives in Forks, Washington with her dad, Charlie (BILLY BURKE), the local chief of police. It's her 18th birthday and she'd seem to have it all, especially with the love of Edward Cullen (ROBERT PATTINSON), a peaceful vampire who, like the rest of his family that includes parent figures Carlisle (PETER FACINELLI) and Esme (ELIZABETH REASER), as well as siblings Rosalie (NIKKI REED), Emmett (KELLAN LUTZ), Alice (ASHLEY GREENE) and Jasper (JACKSON RATHBONE) -- only feed on the blood of animals.
Yet, since they never age, Edward informs Bella that others are becoming suspicious of Carlisle looking too young and thus all of them must move away. Bella wants to go with them, but just as he refuses to turn her into a fellow vampire as she desires, Edward won't allow that and thus breaks up with her.
She's devastated and falls into deep depression, quickly losing contact with her classmates such as Mike Newton (MICHAEL WELCH) and Jessica Stanley (ANNA KENDRICK). Instead, she turns to her childhood friend, Native American Jacob Black (TAYLOR LAUTNER) who enjoys spending time with her, with it quickly becoming obvious his feelings have turned more romantic. But she's still fixated on Edward, especially now that she's found that engaging in any sort of risky behavior cause visions of him to appear to her, warning her to be safe.
That's especially important since two surviving members of a clan of bad vampires, Victoria (RACHELLE LEFEVRE) and Laurent (EDI GATHEGI), want their revenge on the Cullens, and their best and seemingly easiest option is to kill her. While she might appear vulnerable, she has unexpected allies in the form of a small group of werewolves led by Sam Uley (CHASKE SPENCER). Even more shocking to her is that Jacob is now one of them, and he wrestles with his newfound curse and what means regarding their long friendship and his desire to be with her romantically.
At the same time, and while Charlie and his friend Harry Clearwater (GRAHAM GREENE) head off into the woods to find some supposed man-eating bears, Edward is just as forlorn as Bella. Thinking things have taken a turn for the worse, he then decides to take his own life the only way he can, by angering the Volturi vampire royalty and their leader, Aro (MICHAEL SHEEN).
As Bella tries to stop that while sorting out her feelings toward Jacob and Edward, the tension between the werewolves and vampires increases, thus threatening the truce between them.