The Duke nodded.

“It’s an odd thing,” he remarked, “that they should both have been Americans.”

“Heseltine thinks there’s something behind this correspondence,” the Prime Minister said slowly.  “Washington was very secretive about the man Fynes’ identity.  I found that out from Scotland Yard.  Do you know, I’m half inclined to think, although I can’t get a word out of Harvey, that this man Fynes—­”

The Prime Minister hesitated.

“Well?” the Duke asked a little impatiently.

“I don’t want to go too far,” his chief said.  “I am making some fresh inquiries, and I am hoping to get at the bottom of the matter very shortly.  One thing is very certain, though, and that is that no two murders have ever been committed in this city with more cold-blooded deliberation, and with more of what I should call diabolical cleverness.  Take the affair of poor young Vanderpole, for instance.  The person who entered his taxi and killed him must have done so while the vehicle was standing in the middle of the road at one of the three blocks.  Not only that, but he must have been a friend, or some one posing as a friend—­some one, at any rate, of his own order.  Vanderpole was over six feet high, and as muscular as a young bull.  He could have thrown any one out into the street who had attempted to assault him openly.”

“It is the most remarkable case I ever heard of in my life,” the Duke admitted, helping himself to a cigarette from a box which he had just discovered.

“There is another point,” the Prime Minister continued.  “There are features in common about both these murders.  Not only were they both the work of a most accomplished criminal, but he must have been possessed of an iron nerve and amazing strength.  The dagger by which Hamilton Fynes was stabbed was driven through the middle of his heart.  The cord with which Vanderpole was strangled must have been turned by a wrist of steel.  No time for a word afterwards, mind, or before.  It was a wonderful feat.  I am not surprised that the Americans can’t understand it.”

“They don’t suggest, I suppose,” the Duke asked, “that we are not trying to clear the matter up?”

“They don’t suggest it,” his chief answered, “but I can’t quite make out what’s at the back of their heads.  However, I won’t bother you about that now.  If I were to propound Heseltine’s theory to you, you would think that he had been reading the works of some of our enterprising young novelists.  Things will have cleared up, I dare say, by next week.  I am coming round to the House for a moment if you’re not in a hurry.”

The Duke assented, and waited while the secretary locked up the papers which the Prime Minister had been examining, and prepared others to be carried into the House.  The two men left the place together, and the Duke pointed toward his brougham.

“Do you mind walking?” the Prime Minister said.  “There is another matter I’d like to talk to you about, and there’s nowhere better than the streets for a little conversation.  Besides, I need the air.”