The Black Windmill(1974)

Major John Turrant’s (Michael Caine) undercover assignment is immediately compromised after his son is kidnapped. The kidnappers want an exact number of uncut diamonds for his release, a number only discussed and known by a small group of people. John attempts to pay the ransom and recover his son, only to be framed for murder and almost killed.

With no other way to clear his name, John calls every man at the meeting and poses as the kidnapper, telling to meet him. As he lies in wait, a man arrives. As it turns out, Sir Edward Julyan (Joseph O’ Connor) is responsible for the whole mess. Passed over for a promotion and unable to keep up his lifestyle with his much younger wife, he made up the plot to get the diamonds.

John storms the windmill where his son is being held and kills Mckee’s henchman and then Mckee with a Mac-10 machine gun. John recovers his son David and leaves. Sir Edward Julyan is seen still alive, so he is presumably arrested for treason and accessory to kidnapping and murder.