The novel is set in a near-future dystopia in which most people must live in gated communities or in armed nomadic groups called "car families".

The novel traces the experiences of Blake Maslin, a physician living in Southern California, and his sixteen-year-old twin daughters, Rane and Keira.

Rane is decapitated, but Blake manages to escape long enough to infect a long-haul truck driver, making inevitable the spread of the disease through the rest of the country and eventually the world.

Keira, having been cured of leukemia by the microorganism, reluctantly agrees to participate and returns with Eli to the ranch family, pregnant with her own mutant child.

"[1] Brian Stableford argues that the novel and other of her works such as Fledgling hover between parasitism and mutualistic symbiosis since the aliens may confer powers, but at a price.