In Cooties, a mysterious virus hits a small Illinois town affecting only the prepubescent population, transforming them into violent, feral little monsters. The virus centralizes in the town's elementary school, and quickly the infected students have the teaching staff under siege, acting out deadly revenge fantasies with an eerie sense of childlike glee. Finally, the teachers band together, led by a hapless substitute who grew up in the town, realizing they must do the unthinkable if they hope to survive.