Two American college students, David and Jack, backpack across the Yorkshire moors in England. As night falls, they seek refuge in a pub called "The Slaughtered Lamb," where they're met with a cold reception from the locals. Alarmed by the strange behavior of the patrons and the cryptic warnings to stay on the road, avoid the moors, and beware the full moon, the young travelers leave the pub. Disregarding the advice, they wander onto the moors and are attacked by a ferocious beast. Jack is mauled to death while David barely survives, sustaining deep wounds.

David awakens in a London hospital, where he's tended to by nurse Alex. Troubled by nightmarish visions and a visitation from his deceased friend Jack, David is warned that he is now a werewolf, destined to transform at the next full moon. As he grapples with Jack's eerie appearances and the credibility of these supernatural claims, David develops a romantic relationship with Alex, who becomes his compassionate confidante. Unbeknownst to David, his time is running out as the full moon approaches, bringing with it the grim reality of his cursed existence. He finds himself caught between the human world he knows and the horrifying prospect of becoming the very monster that claimed his best friend's life.