riends
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."

"A spy?"

"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."

"Exactly."

"What a pity we did not get th