“To-night by all means,” he declared.  “But my invitation remains —­a challenge!”

CHAPTER XXXI

The Prince, being host, arranged the places at his supper-table. 
Mr. Sabin found himself, therefore, between Lady Carey and a young
German attache, whom they had met in the ante-room of the restaurant. 
Lucille had the Prince and Mr. Brott on either side of her.

Lady Carey monopolised at first the greater part of the conversation.  Mr. Sabin was unusually silent.  The German attache, whose name was Baron von Opperman, did not speak until the champagne was served, when he threw a bombshell into the midst of the little party.

“I hear,” he said, with a broad and seraphic smile, “that in this hotel there has to-day a murder been committed.”

Baron von Opperman was suddenly the cynosure of several pairs of eyes.  He was delighted with the success of his attempt towards the general entertainment.

“The evening papers,” he continued, “they have in them news of a sudden death.  But in the hotel here now they are speaking of something—­what you call more—­mysterious.  There has been ordered an examination post-mortem!”

“It is a case of poisoning then, I presume?” the Prince asked, leaning forward.

“It is so supposed,” the attache answered.  “It seems that the doctors could find no trace of disease, nothing to have caused death.  They were not able to decide anything.  The man, they said, was in perfect health—­but dead.”

“It must have been, then,” the Prince remarked, “a very wonderful poison.”

“Without doubt,” Baron Opperman answered.

The Prince sighed gently.

“There are many such,” he murmured.  “Indeed the science of toxicology was never so ill-understood as now.  I am assured that there are many poisons known only to a few chemists in the world, a single grain of which is sufficient to destroy the strongest man and leave not the slightest trace behind.  If the poisoner be sufficiently accomplished he can pursue his—­calling without the faintest risk of detection.”

Mr. Sabin sipped his wine thoughtfully.

“The Prince is, I believe, right,” he remarked.  “It is for that reason, doubtless, that I have heard of men whose lives have been threatened, who have deposited in safe places a sealed statement of the danger in which they find themselves, with an account of its source, so that if they should come to an end in any way mysterious there may be evidence against their murderers.”

“A very reasonable and judicious precaution,” the Prince remarked with glittering eyes.  “Only if the poison was indeed of such a nature that it was not possible to trace it nothing worse than suspicion could ever be the lot of any one.”

Mr. Sabin helped himself carefully to salad, and resumed the discussion with his next course.