The Avengers.S06E31.Pandora

Tara is kidnapped by two brothers, who drug her and seek to brainwash her into believing that she is Pandora, a young woman she closely resembles, who was once engaged to their elderly father—a retired spy, codenamed the "Fierce Rabbit". He had been a British agent in the First World War, and Tara has to be convinced that she is now living in the year 1915.
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Teleplay by Brian Clemens
Directed by Robert Fuest
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Guest Starring: Julian Glover, James Cossins, Kathleen Byron, John Laurie, Geoffrey Whitehead, Peter Madden, Reginald Barratt