The Avengers: The House That Jack Built

For my money, the first Diana Rigg Avengers season was the high watermark of the series, although the next season (the first in colour) comes very close. Surreal and psychedelic before most people knew what the term meant, the Brian Clemens scripted 'The House that Jack Built' is a fantastic episode, and also looks to have had a bit of an influence on 'The Legend of Hell House'.