Mr. Carlyle’s knowing look expressed:  “Go on, my friend; you are coming to something.”  But he merely contributed an encouraging “Yes?”

“When you emerged just now our second man quietly opened the door of his pen a fraction.  Doubtless he looked out.  Then he closed it as quietly again.  You were not his man, Louis.”

“I am grateful,” said Mr. Carlyle expressively.  “What next, Max?”

“That is all; they are still closeted.”

Both were silent for a moment.  Mr. Carlyle’s feeling was one of unconfessed perplexity.  So far the incident was utterly trivial in his eyes; but he knew that the trifles which appeared significant to Max had a way of standing out like signposts when the time came to look back over an episode.  Carrados’s sightless faculties seemed indeed to keep him just a move ahead as the game progressed.

“Is there really anything in it, Max?” he asked at length.

“Who can say?” replied Carrados.  “At least we may wait to see them go.  Those tin deed-boxes now.  There is one to each safe, I think?”

“Yes, so I imagine.  The practice is to carry the box to your private lair and there unlock it and do your business.  Then you lock it up again and take it back to your safe.”

“Steady! our first man,” whispered Carrados hurriedly.  “Here, look at this with me.”  He opened a paper—­a prospectus—­which he pulled from his pocket, and they affected to study its contents together.

“You were about right, my friend,” muttered Mr. Carlyle, pointing to a paragraph of assumed interest.  “Hat, stick and spectacles.  He is a clean-shaven, pink-faced old boy.  I believe—­yes, I know the man by sight.  He is a bookmaker in a large way, I am told.”

“Here comes the other,” whispered Carrados.

The bookmaker passed across the hall, joined on his way by the manager whose duty it was to counterlock the safe, and disappeared along one of the passages.  The second man sauntered up and down, waiting his turn.  Mr. Carlyle reported his movements in an undertone and described him.  He was a younger man than the other, of medium height, and passably well dressed in a quiet lounge suit, green Alpine hat and brown shoes.  By the time the detective had reached his wavy chestnut hair, large and rather ragged moustache, and sandy, freckled complexion, the first man had completed his business and was leaving the place.

“It isn’t an exchange lay, at all events,” said Mr. Carlyle.  “His inner case is only half the size of the other and couldn’t possibly be substituted.”

“Come up now,” said Carrados, rising.  “There is nothing more to be learned down here.”

They requisitioned the lift, and on the steps outside the gigantic keyhole stood for a few minutes discussing an investment as a couple of trustees or a lawyer and a client who were parting there might do.  Fifty yards away, a very large silk hat with a very curly brim marked the progress of the bookmaker towards Piccadilly.