“Ah!”

“I’ve never met a more innocent looking man, I’ll allow; but if you’ll read the ‘Adventures of Martin Zeda,’ you’ll know that"...

“Tosh!” snapped Dunbar, irritably; “your ideas of psychology would make a Manx cat laugh!  I suppose, on the same analogy, you think the leader-writers of the dailies could run the Government better than the Cabinet does it?”

“I think it very likely"...

“Tosh!  Is there anybody in London knows more about the inside workings of crime than the Commissioner?  You will admit there isn’t; very good.  Accordingly to your ideas, the Commissioner must be the biggest blackguard in the Metropolis!  I have said it twice before, and I’ll be saying it again, Sowerby:  Tosh!”

“Well,” said Sowerby with an offended air, “has anybody ever seen Mr. King?”

“What are you driving at?”

“I am driving at this:  somebody known in certain circles as Mr. King is at the bottom of this mystery.  It is highly probable that Mr. King himself murdered Mrs. Vernon.  On the evidence of your own notes, nobody left Palace Mansions between the time of the crime and the arrival of witnesses.  Therefore, one of your witnesses must be a liar; and the liar is Mr. King!”

Inspector Dunbar glared at his subordinate.  But the latter continued undaunted:—­

“You won’t believe it’s Leroux; therefore it must be either Mr. Exel, Dr. Cumberly, or Miss Cumberly."...

Inspector Dunbar stood up very suddenly, thrusting his chair from him with much violence.

“Do you recollect the matter of Soames leaving Palace Mansions?” he snapped.

Sowerby’s air of serio-comic defiance began to leave him.  He scratched his head reflectively.

“Soames got away like that because no one was expecting him to do it.  In the same way, neither Leroux, Exel, nor Dr. Cumberly knew that there was any one else in the flat at the very time when the murderer was making his escape.  The cases are identical.  They were not looking for a fugitive.  He had gone before the search commenced.  A clever man could have slipped out in a hundred different ways unobserved.  Sowerby, you are...”

What Sowerby was, did not come to light at the moment; for, the door quietly opened and in walked M. Gaston Max arrayed in his inimitable traveling coat, and holding his hat of velour in his gloved hand.  He bowed politely.

“Good morning, gentlemen,” he said.

“Good morning,” said Dunbar and Sowerby together.

Sowerby hastened to place a chair for the distinguished visitor.  M. Max, thanking him with a bow, took his seat, and from an inside pocket extracted a notebook.