When Tory Brennan's mother dies suddenly she is sent to live with the father she has never met on a remote island in South Carolina. Tory might find getting to know her dad difficult, but she has no trouble making friends with the island's other teenage inhabitants: Shelton, Hi and Ben. They quickly form their own gang, united against the snobby pupils of the high school they all attend.

Things change dramatically for them, though, when they rescue a sick wolf-dog puppy who they find locked in a secret cage in a research laboratory. The four nurse him through his illness in their bunker hideout, until he is better. But it's not long before they all fall sick. Could their illness have something to do with the puppy? And why is the head of the laboratory so interested in their health?

Sneaking back onto the island to try to find out what's going on the four are shocked to discover some long-buried human bones. But they are not the only ones wandering on the island that night, and when shots are fired the gang are forced to run for their lives. Suddenly Tory feels she could run all night. Shelton sees more sharply; Hi can smell odours he's never noticed before. And Ben's eyes have changed colour.

Alarmed by the change in each other, they retreat to their bunker. It's clear they have become involved in something fatally dangerous, and somehow they need to discover what is going on before somebody silences them for good. And if what they suspect is true, that somehow they have developed canine capabilities, then harnessing those powers could be the only way to save themselves.