Frame the Baron — John Creasey

The Midi diamonds were not insured. So when they are stolen, it is bad news for their owner - until she manages to enlist the help of John Mannering in their recovery. Mannering - better known as the Baron - has a higher success rate that the police in the business of recovering stolen property, and it is not beyond some disgruntled policemen to believe that he'd had a hand in the thefts in the first place. Soon he is suspected of robbery and, indeed, murder, and he has to strike hard and fast if he is going to clear his name and solve the case.