Two American students, David (David Naughton) and Jack (Griffin Dunne) are backpacking round the Yorkshire moors, when they stumble across a traditional Olde English Pub, affectionately named "The Slaughtered Lamb".
Unfortunately, the locals don't appear too receptive to outsiders, so having chugged down their beverages the two decide to press on. But with darkness falling, they ignore advice to stick to the main road and decide to take a short cut across the moors (never a wise move in a horror film).
When the two are attacked by a strange wolf like creature, only David manages to survive. Awaking to find himself in a London hospital, with no real idea of what's happened, he is befriended by a sympathetic nurse named Alex (Jenny Agutter) who agrees to put him up at her flat until he can make other arrangements.
But his doctor (Played by British actor John Woodvine) is somewhat unsure about the story the locals gave about his injuries, particularly after checking out the village for himself and them denying any knowledge of the incident. Could he really be marked by a werewolf? If werewolves are mythical, why does David keep seeing apparitions of his dead friend Jack warning him what will happen? What is the strange wolf-like creature preying on unsuspecting folk in the London suburbs, and why did David wake up naked in the wolf enclosure at London zoo?
Directed by John Landis, with fantastic special effects by Rick Baker (with none of that CGI stuff that's overused today) and an excellent supporting cast, which includes Brian Glover and the aforementioned Jenny Agutter and John Woodvine, this is an excellent darkly humoured horror film, which is a damnsite better than the many that have followed since.