When the small texas town of Gallup experiences a series of inexplicable bat attacks on local residents, the government calls upon eminent wildlife zoologist Dr. Sheila Casper (
Dina Meyers) to investigate. Although usually a harmless and rather gentle animal, swarms of bats have suddenly become vicious, making Gallup a dangerous place after the sun goes down. Sheila teams up with town sheriff Emmett Kimsey (Lou Diamond Philipps) to discover why these nocturnal mammals have changed their behavior. As the attacks escalate, Sheila and Kimsey must locate and destroy the swarm's cave before the killing spreads.