The Executioner (1970)

Explosive international intrigue results when British Intelligence Agent John Shay (George Peppard) suspects Adam Booth (Keith Michell), a colleague, of being a double-agent. Although Shay's superiors warn him against an investigation, he travels to Greece and Turkey in order to check out his suspicions. There, Shay becomes involved with the beautiful Sarah (Dame Joan Collins), who was once his lover, and is now Booth's wife. Before long, Shay realizes that he is being used as a Communist pawn, and has fallen into grave danger.