“They will take a little thin glass ball of one of these liquids, for instance, hold it in a pocket handkerchief, crush it, shove it under the nose of their victim, and—­whiff!—­the victim is unconscious.  But ordinarily the endormeur does not kill.  He is usually satisfied to stupefy, rob, and then leave his victim.  There is something more to this case than a mere suicide or murder, McBride.  Of course she may have committed suicide with the drugs of the endormeurs; then again she may merely have been rendered unconscious by those drugs and some other poison may have been administered.  Depend on it, there is something more back of this affair than appears on the surface.  Even as far as I have gone I do not hesitate to say that we have run across the work of one or perhaps a band of the most up-to-date and scientific criminals.”

Kennedy had scarcely finished when McBride brought his right fist down with a resounding smack into the palm of his left hand.

“Say,” he cried in great excitement, “here’s another thing which may or may not have some connection with the case.  The evening after Madame arrived, I happened to be walking through the cafe, where I saw a face that looked familiar to me.  It was that of a dark-haired, olive-skinned man, a fascinating face, but a face to be afraid of.  I remembered him, I thought, from my police experience, as a notorious crook who had not been seen in New York for years, a man who in the old days used to gamble with death in South American revolutions, a soldier of fortune.

“Well, I gave the waiter, Charley, the wink and he met me in the rear of the cafe, around a corner.  You know we have a regular system in the hotel by which I can turn all the help into amateur sleuths.  I told him to be very careful about the dark-faced man and the younger man who was with him, to be particular to wait on them well, and to pick up any scraps of conversation he could.

“Charley knows his business, and the barest perceptible sign from me makes him an obsequious waiter.  Of course the dark man didn’t notice it at the time, but if he had been more observant he would have seen that three times during his chat with his companion Charley had wiped off his table with lingering hand.  Twice he had put fresh seltzer in his drink.  Like a good waiter always working for a big tip he had hovered near, his face blank and his eyes unobservant.  But that waiter was an important link in my chain of protection of the hotel against crooks.  He was there to listen and to tip me off, which he did between orders.

“There wasn’t much that he overheard, but what there was of it was so suspicious that I did not hesitate to conclude that the fellow was an undesirable guest.  It was something about the Panama Canal, and a coaling station of a steamship and fruit concern on the shore of one of the Latin American countries.  It was, he said, in reality to be the coaling station of a certain European power