Bella awakens from her transformation from human to vampire, aware of her new abilities, but 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 explains that Bella has had to change in order to survive. He morphs into a wolf, revealing his tribe's shape-shifting power, but does not tell Charlie about vampires.
Several months pass with Carlisle monitoring Renesmee's rapid growth. On an outing in the woods, a bitter Irina sees Renesmee from a distance and believes her to be an immortal child. Immortal children were those who were frozen in childhood, and because they could not be trained nor restrained, they destroyed entire villages. They were eventually executed, as were the parents who created them, and the creation of such children outlawed. Irina goes to the Volturi to report what she has seen. Alice sees the Volturi and Irina coming to kill the Cullens and instructs the others to gather as many witnesses as they can to testify that Renesmee is not an immortal. The Cullens begin to summon witnesses, such as 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.
As some of their potential witnesses are attacked and prevented from supporting the Cullens, Carlisle and Edward realize they may have to fight the Volturi. Their witnesses ultimately agree to stand with them in battle, having realized the Volturi increase the Guard by falsely accusing covens of crimes to gain vampires with gifts. The Volturi arrive, led by Aro, who is eager to obtain the gifted members of the Cullen coven as part of his guard. Aro is allowed to touch Renesmee, and is convinced that she is not an immortal child. Irina is brought forth and takes full responsibility of her mistake, leading to her immediate death. Aro still insists that Renesmee may pose a risk in the future. Alice shows Aro a vision of what will happen in the future if Aro continues to pursue Renesmee.. In the vision, Aro refuses to change his decision and a battle ensues, during which both sides undergo heavy casualties, such as Carlisle, Jasper, and Aro himself.
Two more witnesses then arrive: a man who is a vampire-human hybrid and his aunt who have been living peacefully and undetected for 150 years, proving Renesmee is not a threat. The vampire-human hybrid, whom Jasper and Alice had been searching for, reveals he was fully grown seven years after he was born and hasn't changed since, much to the Cullens' relief. Realizing Renesmee poses no threat and for the sake of self-preservation, a disgraced Aro orders his guards to retreat.
Back at the Cullen home, Alice glimpses into the future, seeing Edward and Bella together with Jacob and a fully matured Renesmee. Edward reads Alice's mind and feels relieved that Renesmee has Jacob to protect her. Alone in the meadow, Bella pushes her mental shield away and finally allows Edward a peek into her mind, showing him every precious moment she and Edward shared together and the two share a kiss.