Bella awakens from her transformation from human to vampire, not only keenly aware of her new abilities, but also of changes within the coven as Jacob has imprinted on her child, Renesmee. It also appears that Bella's father, Charlie, has been attempting to contact the Cullens for updates on Bella's illness. They intend to tell him she didn't survive, which requires that they move out of Forks, Washington to protect their identities. Jacob, desperate not to lose Renesmee, tells Charlie that his daughter is in fact alive and well, and transforms into a werewolf before Charlie to demonstrate that Bella has had to change in order to survive (although not into a werewolf).
Several months pass uneventfully, with Carlisle monitoring Renesmee's rapid growth with Bella, Edward, Jacob and the rest of the Cullen family worrying what will become of her with such a rapid growth rate. On an outing in the woods, a bitter Irina sees Renesmee from a distance, as the immortal child (creating ones is strictly forbidden because immortal children remained mentally on their transformation age, thus being uncontrollable). Irina decides to go to the Volturi for reporting a supposed crime.
Later Alice sees the Volturi and Irina coming to kill the Cullens, and leaves with Jasper the next day, unnoticed, having left a note, where she tells to "gather as many witnesses" as they can before the snow covers the ground because that's when the Volturi will come. The Cullens begin to summon witnesses, including, for example, the Denali family. One of the Denali, Eleazar, later encounters that Bella has a special ability: a powerful mental shield, which she can extend to protect others from mental attacks like Jane's or Alec's ones, with practice.
As some of their potential witnesses are attacked and prevented from coming to support the Cullens, Carlisle and Edward finally face the reality that they may have to fight the Volturi despite their efforts to do otherwise. Some witnesses hesitate, but ultimately agree to stand with them in battle.
The Volturi arrive, led by Aro, who is eager to obtain the gifted members of the Cullen coven as part of his guard. Although Aro is persuaded that Renesmee is not an immortal child, he still insists she poses a risk. Alice and Jasper appear to attest to the existence of other children like Renesmee. After showing Aro a vision of the future, Alice realizes that he will not change his decision. Chaos breaks out and a battle ensues. Both sides undergo heavy casualties, with Aro and most of the Volturi dying. However, the battle is revealed to be Alice's vision, which would come to pass if Aro maintained his pursuit of Renesmee. Two more witnesses then arrive: a fully grown vampire-human hybrid and his aunt, proving Renesmee is not a threat. For the sake of self-preservation, Aro orders his guards to retreat but not without giving one final glance to Alice, Bella and Edward.
Back at the Cullen home, Alice gives us a glimpse into the future: Edward and Bella together with Jacob and a fully matured Renesmee. Edward reads Alice's mind and feels happy that Renesmee has Jacob to protect her. Alone in the meadow, Bella finally allows Edward a peek into her thoughts and as the final lines of the novel read, "And then we continued blissfully into this small but perfect piece of our forever."