“What I know is that Thomery found one of his guests, Princess Sonia Danidoff, in a dead faint in a small drawing-room; that Dr. Marvier declared she had been rendered unconscious; that the theft of a pearl necklace worn by the victim had been the motive of this criminal attempt; that Monsieur Havard, called in at once, first made sure that no one had left the house, and then had everyone on the premises searched... and that is really all I know about it!.. Well, Havard did not find anything?”

“No one was caught with compromising jewels in their possession. The last guest gone, the house searched from top to bottom, not a single pearl had been found. I arrived just when the investigations had terminated: at the moment when they were about to take the Princess home.

She had regained consciousness by this time, and declared she knew nothing except that she had fallen asleep after using a perfume sprayer. This has been seized and chloroform has been found in it; but no one seems to know who filled the sprayer with this stupefying perfume.”

“Did Monsieur Havard send for you?”

“Yes, he telephoned. You know, of course, that I am always asked to intervene now in any ticklish affair!... Well, Dr. Marvier, an expert in his way, noticed that the Princess had been half strangled by the thief in his haste to secure the pearl collar, and he wished me to search for fingerprints on the nape of the victim’s neck – to discover the assassin’s signature, in fact.”

“And there were some?”

“A quantity. The Princess had been slightly wounded in the nape of the neck... blood had been pressed onto the skin of her neck, and it was easy to take a cast of one of the fingers.”

“Was that sufficient?

“Yes, and no; such an impression is something; but there is better than that! The thief must have given the neck a violent squeeze with his hands, consequently there is a complete impression of the hand that I had to get.” Fandor instinctively put his hand to his neck as if he were squeezing it. He said:

“Aren’t such impressions imperceptible?”