Description
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.
Tarrant goes to his wife's home in time to receive a second call from a man identifying himself as Drabble. Drabble demonstrates he knows exactly who Tarrant is and what jobs he does. He instructs him to get Harper to answer the next phone call – making it clear he has Tarrant's son David and is prepared to torture him. Tarrant goes to Harper, and informs him of the situation. Harper agrees to take the phone call and begins to put a surveillance operation into motion – to discover the identity of Drabble. When Drabble gets in touch, he demands that Harper give him £500,000 in uncut diamonds and make a rendezvous in Paris. Harper had recently acquired that exact amount of diamonds to fund another operation he has planned. Harper deduces that Drabble must be acting with information supplied by a member of British intelligence. He immediately begins to suspect Tarrant of staging the kidnapping, and has him placed under observation. Tarrant, meanwhile, has to assign his arms-smuggling case to another officer.
The Drabble gang have placed incriminating evidence into Tarrant's flat, which appears to show a relationship with Celia Burrows, and this is found by Scotland Yard officers conducting a search. This further fuels Harper's belief that Tarrant has in fact arranged the entire kidnapping himself. Harper meets with Tarrant in his office and tells him that he cannot allow the ransom to be met, as the British government does not negotiate with terrorists. Tarrant seemingly accepts this, but when Harper has departed, he breaks into his office and impersonates Harper on a secure telephone – arranging to have the diamonds made available. He then takes them to Paris to make the rendezvous – giving the slip to the tail Harper has placed on him. In Paris he is met by Celia Burrows at the rendezvous. She takes him to a building where it is claimed Tarrant's son is being held.
It soon becomes apparent to Tarrant that Drabble has not got his son there. Instead Drabble makes a cryptic reference to a place in Southern England where there is a view of two windmills. Once he has got the diamonds the ruthless Drabble murders Celia Burrows, and leaves an unconscious Tarrant lying beside the corpse. Tarrant is arrested by the French police – and handed over to Harper and British intelligence. A rescue is then staged by Drabble gang, freeing Tarrant from Harper's custody, but then trying to murder him. Tarrant manages to escape and head back to England. He realises that Drabble meant to try to silence him for good – therefore protecting whoever in British intelligence was supplying him from information. Tarrant then attempts to flush out the traitor, by pretending to be Drabble and arranging a rendezvous at the two windmills with various senior British officers which he now knows to be the Clayton Windmills near Brighton.
The man who comes to the rendezvous is Sir Edward Julyan who is ambushed by Tarrant. Under duress he admits that he arranged the whole thing as he urgently needed large amounts of money to enjoy a comfortable retirement with his free-spending wife. He tries to get Tarrant to accept half the value of the diamonds, but he refuses – and instead demands to know the whereabouts of his son. Julyan tells him that he is being held in the black windmill by Drabble. Tarrant then storms the windmill and rescues his son, killing Drabble and his henchman. He carries David out of the windmill and along the road singing "Underneath the spreading chestnut tree" to him.
