After 17-year-old Sierra Mendez finds the dead body of the water district manager floating down the river, nearly everyone in Los Patos, California, succumbs to a baffling illness that dulls their wits. Phone and internet access are cut off, and the sinister new police chief further isolates the town by putting it on quarantine. When humanoid robots begin to replace the stupefied town residents, Sierra and her friends scramble to stop the deadly plot before it's too late.