Murder at Monte Carlo by E. Phillips Oppenheim

Dalmorres was perhaps a trifle indiscreet in some of his observations in the Sporting Club a few nights later. Every one was inclined to be nervy and irritated. The robbery of the royal jewels of Monaco had turned out to be a more serious affair than was at first believed. It transpired that the whole of the jewels were gone, not a portion of them; that they were valued at fifty millions and that the police were without a single clue as to the bandits. That they were a desperate gang was obvious from their methods. Two of the guards had been shot and the sentry had been stabbed to death in his own box. It was his death cry which had first given the alarm. Servants had streamed out from every direction. There was nothing but an empty safe to be seen. No motor car had been anywhere near the Palace gates. The only clue to the manner by which the thieves had made their escape was furnished by the captain of the guard, who, by throwing himself down and listening with his ear to the ground, believed that he could hear from somewhere in the black distance the rapid beating of a petrol engine driven at great speed.

"These fellows, whoever they are," Dalmorres declared, "have nerve and they have imagination. They work with one another too well to have been brought together haphazard. Neither do I believe that they are French. There's too much method and thoroughness about them."