The Avengers.S05E18.Death's Door

Top civil servants are manipulated into believing that if they go through the door to a vital conference, they will die.
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"Death's Door" is the eighteenth episode of the fifth series of the 1960s cult British spy-fi television series The Avengers, starring Patrick Macnee and Diana Rigg, and guest starring Clifford Evans, Allan Cuthbertson, William Lucas, and Marne Maitland. It was first broadcast in the Grampian region of the ITV network on Wednesday 4 October 1967. ABC Weekend Television, who commissioned the show for ITV, broadcast it in its own regions three days later on Saturday 7 October. The episode was directed by Sidney Hayers, and written by Philip Levene.
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Cast
Patrick Macnee as John Steed
Diana Rigg as Emma Peel
Clifford Evans as Sir Andrew Boyd
Allan Cuthbertson as Lord George Melford
William Lucas as Stapley
Marne Maitland as Albert Becker
Paul Dawkins as Dr. Evans
Michel Faure as Pavret
Peter Thomas as Saunders
William Lyon Brown as Dalby
Terry Yorke as Haynes
Terence Maidment as Jepson