Almost staggered, Harren stared at the Tracer out of his astonished gray
eyes until that gentleman laughed outright and seated himself, motioning
Harren to do likewise.

"Don't be surprised, Captain Harren," he said. "I suppose you have no
conception of our business, no realization of its scope--its network of
information bureaus all over the civilized world, its myriad sources of
information, the immensity of its delicate machinery, the endless data
and the infinitesimal details we have at our command. You, of course,
have no idea of the number of people of every sort and condition who are
in our employ, of the ceaseless yet inoffensive surveillance we
maintain. For example, when your letter came last week I called up the
person who has charge of the army list. There you were, Kenneth Harren,
Captain Philippine Scouts, with the date of your graduation from West
Point. Then I called up a certain department devoted to personal detail,
and in five minutes I knew your entire history. I then touched another
electric button, and in a minute I had before me the date of your
arrival in New York, your present address, and"--he looked up
quizzically at Harren--"and several items of general information, such
as your peculiar use of your camera, and the list of books on Psychical
Phenomena and Cryptograms which you have been buying--"

Harren flushed up. "Do you mean to say that I have been spied upon, Mr.
Keen?"

"No more than anybody else who comes to us as a client. There was
nothing offensive in the surveillance." He shrugged his shoulders and
made a deprecating gesture. "Ours is a business, my dear sir, like any
other. We, of course, are obliged to know about people who call on us.
Last week you wrote me, and I immediately set every wheel in motion; in