“The story which I have to relate,” he began in his careful English, clipping his words a little now and then, “has to do with the theft of the famous Michaelovitch diamonds.  You may, perhaps, remember the case.”

I remembered it, certainly, for the robbery had been conceived and carried out with such brilliancy and daring that its details had at once arrested my attention—­to say nothing of the fact that the diamonds, which formed the celebrated collection belonging to the Grand Duke Michael, of Russia,—­sojourning in Paris because unappreciated in his native land and also because of the supreme attraction of the French capital to one of his temperament—­were valued at something like eight million francs.

“That theft,” continued M. Pigot, “was accomplished in a manner at once so bold and so unique that we were certain it could be the work of but a single man—­a rascal named Crochard, who calls himself also ’The Invincible’—­a rascal who has given us very great trouble, but whom we have never been able to convict.  In this case, we had against him no direct evidence; we subjected him to an interrogation and found that he had taken care to provide a perfect alibi; so we were compelled to release him.  We knew that it would be quite useless to arrest him unless we should find some of the stolen jewels in his possession.  He appeared as usual upon the boulevards, at the cafes, everywhere.  He laughed in our faces.  For us, it was not pleasant; but our law is strict.  For us to accuse a man, to arrest him, and then to be compelled to own ourselves mistaken, is a very serious matter.  But we did what we could.  We kept Crochard under constant surveillance; we searched his rooms and those of his mistress not once but many times.  On one occasion, when he passed the barrier at Vincennes, our agents fell upon him and searched him, under pretence of robbing him.

“He was, understand well, not for an instant deceived.  He knew thoroughly what we were doing, for what we were searching.  He knew also that nowhere in Europe would he dare to attempt to sell a single one of those jewels.  We suspected that he would attempt to bring them to this country, and we warned your department of customs.  For we knew that here he could sell all but the very largest not only almost without danger, but at a price far greater than he could obtain for them in Europe.  We closed every avenue to him, as we thought—­and then, all at once, he disappeared.

“For two weeks we heard nothing—­then came the story of this man Drouet, killed by a stab on the hand.  At once we recognised the work of Crochard, for he alone of living men possesses the secret of the poison of the Medici.  It is a fearful secret, which, in his whole life, he had used but once—­and that upon a man who had betrayed him.”

M. Pigot paused and passed his hand across his forehead.