When a mysterious creature violently kills a man in a Maine lake, Jack Wells (Bill Pullman), the local game warden, looks into the bizarre case, along with Sheriff Hank Keough (Brendan Gleeson) and visiting paleontologist Kelly Scott (Bridget Fonda). Looking for clues in a tooth that the beast left behind, Kelly and the others eventually locate the monster, a massive and vicious reptile eager to devour anything in its path. Can the crocodile-like creature be stopped?