Two American college students on a walking tour of Britain, David and Jack, are attacked by a werewolf in a small village. Jack is killed, and David wakes up in a London hospital. He starts experiencing strange dreams and is visited by Jack's ghost, who warns him that he will transform into a werewolf at the next full moon. David falls in love with his nurse, Alex, but struggles with the growing realization that he is capable of committing violent acts. As the full moon approaches, David transforms into a werewolf and goes on a killing spree. Eventually, David is shot and killed by the police.

An American tourist encounters a secret society of werewolves in Paris and becomes one himself. With the help of a French woman, he tries to find a cure for his condition while being hunted by both werewolves and the police.