'Don't Look Behind You' by Brian Clemens

Mrs. Gale is invited to spend the weekend at the home of Sir Cavalier Resagne, an expert in mediaeval clothing. Once there, she is greeted by a strange girl named Ola, who tells her that Sir Cavalier has gone away for the evening. When Ola is also called away, it soon becomes clear that Mrs. Gale is being watched. Besieged by bizarre incidents and harrowing experiences, Mrs. Gale eventually discovers that an old enemy is behind the disturbing activity; the man believes her to have broken his heart, and now he is stalking her with murderous intentions...

Patrick Macnee (John Steed), Honor Blackman (Cathy Gale), Janine Gray (Ola), Kenneth Colley (Young Man), Maurice Good (Man)*
*The villain is credited on-screen as simply ‘Man’, although both Mrs. Gale and Steed clearly refer to him as Martin Goodman several times in the episode.

Directed by Peter Hammond
Produced by John Bryce

TX:
UK: 14th December, 1963

Notes:
*Featuring John Steed and Mrs. Cathy Gale

*Working title: 'The Old, Dark House'

*This episode is later remade as ‘The House That Jack Built ‘ in season 4, and ‘The Joker’ in season 5