and therefore used for making hurried notes for quick
reference.

To the inexpert person the combination of letters and figures
gave a bewildering appearance to the notes, but it did not
actually make the cipher any more intricate.

You can readily make up your own key to this cipher by
writing out the letters of the alphabet from A to Z. Under
these letters you again write the letters of the alphabet,
placing the letter A under the letter Z and working backward.
By this arrangement, A would stand for Z and Z for A. Below
This you again write out the letters of the alphabet, and under
these, beginning at Z and working backward, write the numbers 1
to 10, which brings you to the letter Q. From P to J you write
the figures 20 to 26 and from I to A you write the figures 30
to 38. The person using this cipher probably memorized these
two arrangements. In writing a word of say six letters, he
would use four letters and two figures. To anyone glancing at
his notes in a casual way, the system looked intricate, but to
him these notes could be read almost as easily as if written in
plain English.

Attached to the letter were several pages containing the decoded
notations from the book. After carefully reading these, Marsh folded
the sheets and started to place them in his pocket. Then he paused,
glancing about the room thoughtfully. A moment later he smoothed the
sheets out flat and lifting up the corner of the rug, slipped them
under it well toward the center. Walking back and forth over the
spot several times, he seemed satisfied. Then he turned up one of
the chairs, placed the notebook inside of the bottom lining, and
putting on his hat and coat, went out.

CHAPTER XVIII

THE ENEMY SHOWS HIS HAND

After returning from supper, Marsh sat down to look over the evening
paper. The Merton case, which had replaced the Sheridan Road mystery
in editorial esteem, was now retired to an inner page. He read the
usual short notice that the police expected to have the guilty
parties in custody within the next twenty-four hours, accompanied by
an announcement of some of their plans so that the people sought
could have timely warning of what to expect. Then he turned to other
news of the day and the time slipped by.

About nine o'clock Marsh raised his head and listened. He had
distinctly heard two sharp reports, like pistol