The Black Windmill

The Black Windmill is a 1974 British spy thriller directed by Don Siegel and starring Michael Caine, John Vernon, Janet Suzman and Donald Pleasence. It was produced by Richard D. Zanuck and David Brown.

Two schoolboys are playing with a model plane on an abandoned military base in the English countryside. They are approached by two RAF personnel who rebuke them for trespassing, and take them to see their commanding officer. It soon becomes apparent that they are not really in the military and the two boys are kidnapped.In London a British intelligence officer, Major Tarrant, is engaged in an undercover operation to try to infiltrate a gang of arms smugglers who are selling weapons to terrorists in Northern Ireland. He makes an initial approach with Celia Burrows, a member of the organisation. He arranges to come back the next week to meet her boss. He then heads to a large country house, where the head of MI6 Sir Edward Julyan lives, and makes a report about his operation to Julyan and his direct superior, Cedric Harper. While he is there he receives a telephone call from his wife who tells him their son David has been taken and she has received a strange phone call. Tarrant reacts calmly, revealing to his superiors only that he has a family problem, and is given permission to leave. ........

Source: Wikipedia