Breaking Dawn is divided into different parts. The first part details Bella's marriage and honeymoon with Edward, which they spend on Isle Esme, a private island off the coast of Brazil that Carlisle owns. Two weeks into their honeymoon, Bella realizes that she is pregnant. Because the fetus is part-vampire, her condition progresses at an unnaturally accelerated rate. Bella and Edward immediately return home to Forks, Washington, where the fetus continues to develop at an abnormal speed, causing Bella severe physical and emotional distress.
The second part of the book is written from the perspective of Jacob Black, a Quileute Native American who, like other members of his tribe, can shapeshift into a wolf. Knowing of Bella's wish to become a vampire, he is immediately suspicious when she returns from her honeymoon and the Cullens keep her father, Charlie, from seeing her. Believing the Cullens have broken their treaty not to bite another human, he advances on their home intending to kill Edward. He arrives and discovers that Bella is undergoing a difficult pregnancy in which the fetus is draining her life away. Jacob begs Bella to abort the fetus to save her life, as neither Carlisle, a doctor, nor Alice who can see the future, are optimistic about Bella's prognosis.
Despite concerns that her pregnancy will be fatal, Bella is determined to continue it, believing she can survive long enough to give birth and then be transformed into a vampire. As the wolves are telepathic, they hear Jacob's thoughts about Bella. Fearing Bella will give birth to an uncontrollable, bloodthirsty child, they want to kill her and the fetus. Jacob accepts his bloodline as the true pack leader in order to break free from the alpha, Sam's control. He goes to warn the Cullens that the wolf pack plans to kill Bella. En route to the Cullens, Seth Clearwater, a younger pack member, also breaks away and joins Jacob. He notes that once they formed their own pack, they can no longer hear the other wolves' thoughts. They patrol the Cullens' property and soon after Leah, Seth's older sister and the lone female wolf, joins them.
Bella enters labor as the baby begins fighting its way out, breaking her body. Edward is forced to perform a cesarean section, saving the baby. As Bella is dying, Edward injects his venom into her heart. Jacob, believing Bella is dead, blames Bella's infant daughter Renesmee. He goes to kill the infant but instead imprints (an involuntary response in which a shape-shifter finds his soul mate) on her.
The third section shifts back to Bella's perspective, describing her painful transformation, finally waking to find herself changed into a vampire. Fully recovered, she enjoys her new life and vampire abilities. Renesmee grows rapidly into a toddler and is spotted at a distance by Irina, a vampire from the Alaskan coven. Misidentifying her as an "immortal child," a human child who has been turned into an uncontrollable vampire, Irina presents her allegations to the Volturi who outlawed the creation of such creatures. As the largest and most powerful vampire coven, the Volturi see Renesmee and the Cullens as a threat and plot to destroy them. Foreseeing their arrival, the Cullens gather other vampire clans from around the world to stand as witnesses and prove to the Volturi that Renesmee is not an immortal child upon Alice's request. Jacob's imprinting on Renesmee has forged an unbreakable bond and mutual protective pact between the Cullens and the Quileute, ending the hatred between them. As local and foreign vampires arrive, the Cullen house becomes the headquarters and training ground for the assorted vampires and the Quileute wolf packs. Bella learns that she is a 'shield', meaning the gifts of other vampires do not work on her, which is why Edward and Aro cannot read her mind. Bella works with the other vampires to improve her skill and shield people other than herself.
Upon confronting the gathered Cullen allies and witnesses, the Volturi discover that they were misinformed on Renesmee's identity. The Volturi execute Irina in an attempt to instigate a full battle but are unsuccessful. They bring up the Cullens' pact with the Quileute wolves and the uncertainty of Renesmee's future in an effort to further provoke hostilities, naming her as a threat to the secret existence of vampires. Alice and Jasper, who left prior to the gathering of the Cullen's allies, return with a Mapuche called Nahuel, a 150-year-old vampire-human hybrid like Renesmee. Alongside him is his biological aunt, Huilen, who explains that her sister fell in love with a vampire and became pregnant with his child, though she died in childbirth. When Nahuel was born, he bit his aunt and made her immortal. Nahuel proves that hybrids pose no threat, and the Volturi agree to leave the Cullens alone. The Cullens and their allies return to their homes in peace, realizing that the Volturi may one day return. When Bella is alone with Edward, she allows him to read her mind for the first time and shares her feelings about him.
