A small town is thrown into chaos when a spaceship crashes in the nearby woods, leaking radiation that mutates native mosquitos into giant, deadly predators. These enormous insects begin to terrorize the residents, attacking and killing with their now formidable size and strength. Among those affected is a park ranger named Megan, who discovers the initial signs of the infestation while on her patrol. As the body count rises, Megan teams up with two escapees from a local prison, Earl and Junior, who have a unique understanding of the terrain and survival skills that prove invaluable. They also cross paths with a couple of forest rangers and an ornithologist named Ray, who is desperate to uncover the source behind the mutation.

Together, Megan, Earl, Junior, Ray, and the rangers form a ragtag group that devises multiple plans to fend off the giant mosquitos and protect themselves and any remaining survivors. Their journey involves navigating through dense forests and abandoned structures while staying one step ahead of the relentless swarm. Tensions rise as resources dwindle and it becomes clear that the monsters are growing increasingly aggressive. The group faces numerous challenges and must make life-or-death decisions as they seek a way to stop the mutant mosquitos before the entire area becomes uninhabitable.