Landis wrote the first draft of the screenplay for the film in and shelved it for over a decade. Prospective financiers believed that Landis's script was too frightening to be a comedy film and too humorous to be a horror film. Since its release, it has become a cult classic. As night falls, they stop at the Slaughtered Lamb, a local pub. Jack notices a five-pointed star on the pub's wall. When he asks about it, the pub-goers grow hostile, prompting him and David to leave.
The pub-goers warn the pair to keep to the road, stay clear of the moors, and beware of the full moon. David and Jack wander off the road and onto the moors, where a vicious creature attacks them. Jack is mauled to death and David is seriously injured. The beast is shot and killed by some concerned pub-goers who followed the pair. Instead of an animal carcass, David sees a nude dead man lying next to him before passing out. David wakes up three weeks later in a London hospital.
Inspector Villiers interviews David and informs him that the locals reported that an escaped lunatic attacked him and Jack. David insists a rabid dog or wolf attacked them. An undead Jack later appears to David and explains that they were attacked by a werewolf ; since David was bitten, he is now a werewolf too. Jack is cursed to walk the earth in limbo, neither dead nor alive, until the wolf's bloodline is severed.
Jack urges David to kill himself before the next full moon so he does not harm anyone. Hirsch visits the Slaughtered Lamb to investigate, suspecting that David might have been influenced by local superstitions.
When asked about the incident, the pub-goers deny any knowledge of David, Jack, or the attack. However, one distraught pub-goer privately tells Dr. Hirsch that David will endanger other people when he transforms. Upon being released from the hospital, David stays with Alex Price, the young nurse who cared for him. Alex tells David that she is worried about his mental state. Jack, now even more decayed, appears and warns David that he will become a werewolf the following night, and again advises him to commit suicide.
