“You think it possible that the Nastirsevitch affair is the work of one lot, and the Lennard affair the work of another?” asked Allerdyke, thoughtfully.  “In that case, I’ll ask you a question, Mr. Delkin.  How do you account for the fact that my cousin James, the Frenchwoman, Lisette Beaurepaire, and his valet, Ebers, or Federman, or Herman, were all found dead under similar circumstances?  Come, now!”

“Aye, but were they?” demanded Delkin, clapping his hands together with a smile of triumphantly suggestive doubt.  “Were they?  You don’t know—­and the expert analysts don’t know yet, and perhaps never will.  I’ll grant you that there’s a strong probability that Ebers and the French maid were victims of the same murderer; but that doesn’t prove that your cousin was.  No, sir!—­my impression is that everybody is taking too much for granted.  And whether it offends you or not, Fullaway—­and my intention’s good—­you ought to make drastic researches into your office procedure—­you know what I mean.  The leakage of the secret, sir, came from—­there!”

Fullaway rose.

“Well, I shan’t do any good by sitting here,” he said, a little huffily.  “If I’m going to begin those drastic researches I’d better begin.  Coming, Allerdyke?”

The two men walked away together after taking leave of the millionaire and the Princess.  But before they were clear of the courtyard, Chilverton caught them and tapped Fullaway on the elbow.

“Say!” he said confidentially.  “You won’t mind my asking you—­who’s this Van Koon that you mentioned?”

“Man from our side who’s been here in London all this spring,” answered Fullaway promptly.  “He was coming with Allerdyke and me just now, but he turned back—­just when you and Delkin drove in here.”

Chilverton gave Fullaway a quick look.

“Did he see me?” he asked.

“Sure!” replied Fullaway.  “Asked who you were—­or I did.”

“You did,” remarked Allerdyke.  “Then he went off.”

“Describe him,” said Chilverton.  He listened attentively while Fullaway gave him a sketch of Van Koon’s appearance.  “Um!” he continued.  “Do you mind my walking to your hotel with you?  I believe I know that man, and I’d like to see him.”

A hall-porter was standing at the door of the Waldorf who had been there when the three men went out together at one o’clock.  Fullaway beckoned him.

“Seen anything of Mr. Van Koon?” he asked.

“Mr. Van Koon?—­yes, sir.  He came back a few minutes after you and Mr. Allerdyke and he had gone out, got a suit-case from upstairs, left word that he’d be away for the night, and went off in a taxi, sir,” answered the man.  “Seemed to be in a great hurry, sir!”

Before Fullaway could speak, Chilverton seized the hall-porter’s arm.  “Did you hear him give the cab-driver any direction?”

“Yes, sir,” replied the man promptly.  “St. Pancras Station, sir.”