It's a hot summer in New York City, Fourth of July celebrations are looming and mangled bodies are beginning to turn up in the river. Nick Hartfield (Michael Reilly Burke) is the police officer who slowly gathers clues that add up to one unbelievable conclusion: A giant octopus has been on the prowl in the waters surrounding the city. His superiors, however, don't heed what they consider to be the ramblings of a madman, and thus the city suffers more blows from the monster's deadly tentacles.