The Avengers.S04E21.A Touch of Brimstone

An eccentric band of libertines (called the Hellfire Club) who commit deadly practical jokes is revealed to have much bigger plans in mind.
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This episode contains visual reference to sado-masochistic pornography, and features Rigg wearing a kinky "Queen of Sin" costume, which she designed herself. Consequently, it was not shown on American television; a scene where Peter Wyngarde's character The Honorable John Cleverly Cartney attempting to whip Peel was cut down for some UK screenings. "A Touch of Brimstone" was the most watched episode of The Avengers on its original showing.
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Teleplay by Brian Clemens
Directed by James Hill
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Guest Starring: Peter Wyngarde, Carol Cleveland, Colin Jeavons, Jeremy Young, Steve Plytas, Alf Joint, Robert Cawdron