 When a local begins fishing with dynamite in Bog Lake, something a bit larger pops to the surface: a green, bug-eyed mutant monster awakened from a long sleep, which promptly begins killing and eating fishermen who stumble across its lair. When biologist Ginny Glenn (Gloria DeHaven) discovers the creature s evolutionary nature, the local sheriff (Aldo Ray) decides to use most methods to destroy the tenacious beast.