In early 1920s New York, a young man is befriended by a neighborhood mobster. He learns the trade then decides to go straight and join the police force. It isn't long before he uses his connections to destroy the mob from within.

Doctor Baines has been conducting genetic experiments on piranhas and has made them virtually unstoppable. Unfortunately, his assistants, Maggie and Paul, accidentally release the hybrids into the Lost River Lake threatening to destroy everyone in their path. Can they prevent the flesh-eating piranhas from escaping into the ocean and spawning?