Snakehead fish invade Cultus Lake in the small town of Cultus, Maryland, although the town's police department poisons the lake, seemingly killing all of the fish. Two years later, bodies begin showing up in the lake, with town sheriff Patrick James temporarily closing off the lake. After Patrick's daughter Amber's boyfriend James, and James' friend are eaten by unseen creatures, the bodies are inspected, and local doctor Jenkins gives Patrick a tooth he found in one of the bodies. Patrick attempts to convince the town's mayor to shut down the lake, although to no avail, as the town is suffering from economic troubles.