Svengoolie

The Beast Must Die (11x13)

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When big-game hunter Tom Newcliffe (Calvin Lockhart) invites a group of people to stay at his estate, they expect a relaxing weekend. Instead, they arrive to learn he thinks one of them is a werewolf and that no one can leave until that person is exposed. Among the suspects are a piano player (Michael Gambon) and his girlfriend (Ciaran Madden), an archaeologist (Peter Cushing), a diplomat (Charles Gray) and an artist (Tom Chadbon), all of whom are subjected to a series of werewolf tests.