Clare Campbell has worked hard to create distance between herself and her troubled family. But when she receives news of her parents' murder, she's forced to return to the quiet town of Clarkeston, Maine, to arrange their funeral and take legal guardianship of her unpredictable and mentally ill brother, Wes.

While Clare struggles to come to grips with the death of her parents, a terrifying pathogen outbreak overtakes the town. She is all too familiar with the resulting symptoms, which resemble those of her brother's schizophrenia: hallucinations, paranoia, and bizarre, even violent, behavior. Before long, the government steps in--and one agent takes a special interest in Wes. Clare must make a horrifying decision: save her brother or save the world.