The Silver Mistress by Peter O'Donnell

Sir Gerald Tarrant, head of a secret service department in the British Government, and good friend of Modesty Blaise, is being driven through the south of France. His chauffeur stops to help two nuns change a tire on their car, but it is a trap. Sir Gerald is taken prisoner - by the kidnappers, posing as holy sisters.

An eyewitness convinces Modesty Blaise that Sir Gerald needs her help, and that the discovery of his car at the bottom of a gorge was a hoax. Sir Gerald is not dead, but rather a prisoner. Modesty and her trusty lieutenant Willie Garvin will find that they have met their match when they mount a rescue, and come up against Mrs McTurk, a ferocious assassin, and Mr Sexton, the world's greatest exponent of unarmed combat.

To escape, Modesty must defeat the invincible Mr Sexton in a final confrontation deep underground in the Lancieux caves. Can she survive?