In the near future, Norton Horton, eighteen, resident of Bellingham, Washington, lives with a virus that causes his flesh to decay in sunlight. As a member of a newly designated class call Melters, jobs are scarce, and prejudice is rampant.

However, he's given another chance when a friend from high school, Vanessa Ness, offers him a chance—through her father—of controlling his condition.

Her father, Franklin Ness, is a researcher at Grimmer Industries, a company that has developed a new vaccine. Norton is the first recipient, and to his relief it works—but only for a week. Repeated injections are needed.

While Norton enjoys his new life, he meets his ex-girlfriend, Denise. Denise is part of the Dwellers, those who've devolved into a half-human, half-beast combination, due to the virus. She still remembers him, and he vows to help her.

Searching for a solution, he stumbles across Doctor Ness's notes. To his horror, Norton finds out that he wasn't the first recipient of the vaccine—the Dwellers were. Furthermore, due to Ness's experiments, some of them have sunk even lower to a monstrous state that the press calls the Regressed.

Ness and the army intend to use the Regressed as weapons to terrorize any enemy that threatens America, and they'll kill to keep their secret safe.

With a newfound mission, Norton descends into the sewers, brings Denise out with the help of the vaccine, and together, they start their own private war to bring the truth to the people—or die trying.