“I was looking out for loiterers in the street, but I saw none. We are dealing with a clever man, Watson. This matter cuts very deep, and though I have not finally made up my mind whether it is a benevolent or a malevolent agency which is in touch with us, I am conscious always of power and design. When our friends left I at once followed them in the hopes of marking down their invisible attendant. So wily was he that he had not trusted himself upon foot, but he had availed himself of a cab so that he could loiter behind or dash past them and so escape their notice. His method had the additional advantage that if they were to take a cab he was all ready to follow them. It has, however, one obvious disadvantage.”

“It puts him in the power of the cabman.”

“Exactly.”

“What a pity we did not get the number!”

“My dear Watson, clumsy as I have been, you surely do not seriously imagine that I neglected to get the number? No. 2704 is our man. But that is no use to us for the moment.”

“I fail to see how you could have done more.”

“On observing the cab I should have instantly turned and walked in the other direction. I should then at my leisure have hired a second cab and followed the first at a respectful distance, or, better still, have driven to the Northumberland Hotel and waited there. When our unknown had followed Baskerville home we should have had the opportunity of playing his own game upon himself and seeing where he made for. As it is, by an indiscreet eagerness, which was taken advantage of with extraordinary quickness and energy by our opponent, we have betrayed ourselves and lost our man.”

We had been sauntering slowly down Regent Street during this conversation, and Dr. Mortimer, with his companion, had long vanished in front of us.

“There is no object in our following them,” said Holmes. “The shadow has departed and will not return. We must see what further cards we have in our hands and play them with decision. Could you swear to that man’s face within the cab?”

“I could swear only to the beard.”

“And so could I—from which I gather that in all probability it was a false one. A clever man upon so delicate an errand has no use for a beard save to conceal his features. Come in here, Watson!”

He turned into one of the district messenger offices, where he was warmly greeted by the manager.

“Ah, Wilson, I see you have not forgotten the little case in which I had the good fortune to help you?”

“No, sir, indeed I have not. You saved my good name, and perhaps my life.”

“My dear fellow, you exaggerate. I have some recollection, Wilson, that you had among your boys a lad named Cartwright, who showed some ability during the investigation.”