We hurried together down the stairs and into the street. Dr. Mortimer and Baskerville were still visible about two hundred yards ahead of us in the direction of Oxford Street.
"Shall I run on and stop them?"
"Not for the world, my dear Watson. I am perfectly satisfied with your company if you will tolerate mine. Our friends are wise, for it is certainly a very fine morning for a walk."
He quickened his pace until we had decreased the distance which divided us by about half. Then, still keeping a hundred yards behind, we followed into Oxford Street and so down Regent Street. Once our friends stopped and stared into a shop window, upon which Holmes did the same. An instant afterwards he gave a little cry of satisfaction, and, following the direction of his eager eyes, I saw that a hansom cab with a man inside which had halted on the other side of the street was now proceeding slowly onward again.
"There's our man, Watson! Come along! We'll have a good look at him, if we can do no more."
At that instant I was aware of a bushy black beard and a pair of piercing eyes turned upon us through the side window of the cab. Instantly the trapdoor at the top flew up, something was screamed to the driver, and the cab flew madly off down Regent Street. Holmes looked eagerly round for another, but no empty one was in sight. Then he dashed in wild pursuit amid the stream of the traffic, but the start was too great, and already the cab was out of sight.
"There now!" said Holmes bitterly as he emerged panting and white with vexation from the tide of vehicles. "Was ever such bad luck and such bad management, too? Watson, Watson, if you are an honest man you will record this also and set it against my successes!"
"Who was the man?"
"I have not an idea."
"Well, it was evident from what we have heard that Baskerville has been very closely shadowed by someone since he has been in town. How else could it be known so quickly that it was the Northumberland Hotel which he had chosen? If they had followed him the first day I argued that they would follow him also the second. You may have observed that I twice strolled over to the window while Dr. Mortimer was reading his legend."
"Yes, I remember."
"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."
"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.