Carnaby and the Kidnappers — Peter N. Walker

Three girls, each the daughter of a British Member of Parliament were kidnapped, abducted by open force. Then came murder and blackmail. Carnaby began working on his own, and the only way to lure the kidnappers into the open was for the police to take the initiave - with Carnaby as bait. No-one could be allowed to blackmail the British authorities, even if it meant death for the victims - but Carnaby was a policeman, and policemen were dispensible.