Bella Swan, newly graduated from high school, marries her vampire soul mate, Edward Cullen. They honeymoon on a remote tropical island for several weeks. When Bella feels ill and realizes she’s pregnant, Edward rushes her home. The Cullens have never heard of a vampire-human hybrid, so they worry about what sort of monster might be growing inside Bella at such an alarming rate. Edward promises that Dr. Carlisle Cullen will “take care of” the preborn child, but Bella refuses to go through with the abortion. The baby breaks her bones and seems to be killing her from within. On a hunch, Dr. Cullen gives Bella human blood to drink. Once Bella begins this regimen, the baby becomes more cooperative.
Bella’s best friend, Jacob, is repulsed to learn she’s allowing a monster to grow inside of her. Jacob is a Quileute Indian. His tribesmen have been mortal enemies of vampires for generations. Some Quileutes, including Jacob, turn into wolves when they sense danger from vampires. Though the Quileutes and Cullens have worked together in the past to protect Bella, the unknown creature in Bella’s womb now makes the tribe nervous.
Sam, the leader of the wolf pack, wants to protect the tribe and the town by attacking the Cullens and destroying the fetus. While Jacob loathes the baby that’s killing Bella, he loves his friend and wants her to be happy. He breaks off from the wolf pack, inadvertently starting his own pack when Seth Clearwater and his sister, Leah, submit to his leadership. The three patrol the area around the Cullens’ home to protect Bella and the other vampires from wolves.
After a short gestation period, Bella begins to vomit blood. The baby can’t breathe, and Bella is near death. Jacob administers CPR to Bella while Edward chews through her skin and the thick coating surrounding the baby. Renesmee (named for Bella’s and Edward’s mothers, Renee and Esme) emerges healthy and beautiful. The only way for Edward to save Bella from death is to force his venom into her system and turn her into a vampire. When his efforts seem to have failed, and they think Bella is gone, Jacob rushes downstairs where Renesmee sleeps. In his fury, he prepares to destroy the child. But when he looks in her face, a Quileute magic called imprinting takes over. Jacob realizes he has met his soul mate. Jacob’s imprinting on Renesmee also means the Quileutes must no longer attempt to harm the baby.
Bella’s heart stops, but Edward has successfully changed her into a vampire. After enduring days of excruciating pain, Bella is able to test out her new body. The Cullens keep her away from humans, including Renesmee, until they learn how she will react. Bella proves less volatile and more controlled than most newborn vampires. She can interact safely with her daughter, Jacob and other humans. Bella is thrilled with her beautiful, strong, new body. She learns to hunt large animals like the other Cullens (who try to be civilized and refrain from eating humans). She and the others remain concerned about Renesmee growing at such a rapid pace. Carlisle tries to research this phenomenon to estimate how quickly Renesmee will become full-grown and how long she’ll live.
One day, a vampire named Irina sees Bella, Jacob and Renesmee hunting in the woods. Viewing them from a distance and recognizing Bella, Irina assumes Renesmee is an immortal child. The Volturi ordered long ago that all immortal children — people turned into vampires during childhood — must be destroyed. Alice, Edward’s sister-in-law, foresees that Irina will tell the Volturi what she thinks she’s seen. The Volturi will then come to Forks to mete out justice. The Cullens quickly contact their vampire friends around the globe, asking them to come meet Renesmee. In order to avoid a battle, they need their friends to bear witness to what Renesmee is before the Volturi strike. The Cullens’ home soon teams with dozens of vampires from around the world. The Volturi arrive, as Alice predicted, with their full army and entourage. A tense and lengthy stand-off ensues. Even when the Volturi concede that Renesmee is not an immortal child, they still consider destroying her since they don’t know if she is a danger to the vampire lifestyle. Just when a battle seems imminent, Alice and her soul mate, Jasper Cullen, arrive with a vampire woman and her nephew, Nahuel. Nahuel is a human-vampire hybrid like Renesmee, the only one that the vampires have ever seen. He not only offers proof that hybrids pose no danger, but he brings hope to Jacob and the Cullens concerning Renesmee’s lifespan. Nahuel became fully mature at 7 years but has continued to live for several hundred years. The Volturi recognize their defeat and return to Italy.