In the town of Ojen Marsh, Iowa, an epidemic begins: the local water contains toxins that turn a person insane immediately after ingestion. David (Timothy Olyphant), the town’s sheriff, tries to figure out what’s going on, having gathered a small group of uninfected people, including his doctor wife (Rada Mitchell). But to survive in a city full of crazy people is not the most difficult test for the heroes. The real nightmare begins when a military detachment arrives at the site of the infestation.