Vivian is a loup-garou, or werewolf, though that term is rarely used. This (non-human) species gains the power to transform into a wolf-like creature (the name is never mentioned, though it is said not to be a wolf) as the full moon approaches; the nearer the full moon, the easier the transformation. On the night of the full moon, however, the loup-garou must transform. The transformation can be held back for a few minutes or so, but it takes a toll on the loup-garou, often resulting in nausea and fatigue. Loup-garou cannot reveal their identity for fear of extinction. Silver kills them if it touches an open wound.

Vivian retains a generally wolf-like personality in human form; she is extremely stubborn and has no human friends. She meets a boy named Aiden and slowly falls for him. Unfortunately she is named as the mate of the pack leader, Gabriel. Though she is unwilling to cooperate, Gabriel refuses to give up "courting" her. The pack assumes she will come around, but until she does, she is considered suspicious due to her friendship with humans. Vivian is left to choose between Aiden and the trust of her pack. Gradually more members of her pack enter the story, and it is revealed that the other five young male loup-garou have been killing humans, an act forbidden by the Law of the Moon: Any loup-garou that kills a human faces death. Vivian later reveals her true form to Aiden. Seeing his terror, Vivian leaps from his bedroom window, lands on her feet and runs off.

She wakes up in her own bed, with blood on her nails and no memory of what happened. In the news, a man was killed by a wolf-like animal. Similar incidents continue to occur, until she finds a human hand on the floor of her bedroom. Vivian realizes that all of the clues point to her as the rogue. She then decides to commit suicide for the sake of the pack; but before she does, the pack leader, Gabriel, informs her that it wasn't she who killed the humans. One of the Five, Rafe, and his lover, Astrid, were tricking her. They had set everything up so that she would be blamed.

They proceed to the final showdown. Aiden was tricked into coming - he shoots Rafe with a silver bullet as Vivian attacks Astrid. After Gabriel kills Astrid, he approaches Aiden who shoots at him in terror. Vivian leaps in front of him, taking the bullet for Gabriel. The pack's healer is summoned, who manages to get the silver bullet out fast enough to save Vivian's life, but she is trapped between her two forms.

Later, Gabriel enters Vivian's bedroom, who is mourning about being trapped between forms. The pack leader explains his past, telling Vivian that he once loved a dancer who he ended up killing. They bond, and share a kiss, and Vivian is finally able to transform again. The books ends with Vivian becoming the alpha female.