Given the below context:  John Shay, a British MI5 agent, had grown up in the United States, and who was nearly killed while on assignment abroad. Convinced that he was framed, he returns to London to uncover the mole responsible for the set-up. John Shay suspects that his colleague Adam Booth is a Russian spy. The action takes place in London, Athens, Istanbul and Corfu, where Shay goes in his investigation trying to gather evidence that Booth is a double agent. When Shay's superiors are not convinced, and even after a special hearing clears Booth of any wrongdoing, he takes matters into  his own hands and executes Booth.Shay assumes the identity of Booth, and, with the assistance of Booth's widow Sarah and his own girlfriend Polly, he launches into an investigation to uncover Booth's connections. Shay maintains a romantic relationship with both women. Booth's wife is the romantic interest of Shay and British scientist Philip Crawford, who provided information to Shay about Booth being a double agent. Shay's superiors are Col. Scott and Vaughan Jones. Polly assists him in his investigations by providing him with information apparently confirming his suspicions.Shay finds a plane ticket in Booth's pocket which he then uses to fly to Athens along with Booth's widow, who is unaware that her husband has been murdered by Shay. Upon arrival in Athens, Shay assumes Booth's identity and subsequently goes to Corfu, where he is captured along with Sarah by Soviet agents who want Crawford in return for the freedom of their captives. A CIA agent under the name of Professor Parker manages to free them both. Colonel Scott (Shay's superior) reveals that Sarah's husband was indeed a double agent who was used by MI5 to supply the Soviets with false information.  Guess a valid title for it!
The Executioner (1970 film)