by
matter memorandum arrange for yacht mooring on east river instead of
north after wednesday eighth job finis memorandum settle telephone
exchange proceeds not later than monday paid electrician special wiring
two hundred in full settlement."

"There, Miss Helene, how do you like my little game of letter building?"

There was a boyish gleam of triumph in his smile as he turned toward
her.

"You are a wizard, but how did you work it all out?" There was no
smile in her face, only a mingled horror at the revelations of this
calculating monster in his businesslike murder work, and an unfeigned
admiration for Shirley's keenness.

"A very old method, but one which would have availed for naught without
your help. The letter paper which you used and the unmistakable identity
of Warren's machine are two more bars of iron with which to imprison
him. The paper of that note is the same on which they wrote to Van
Ceft for money, and their threats to me. This shows from a microscopic
examination of its texture. I will give the whole book to a trustworthy
stenographer: more than six months of these little confessions are
tabulated here. Warren was evidently so used to this code that he could
write in it as easily as I do with the straight alphabet. His training
in German universities developed a thoroughness, a methodical recording
of every thing, which is apt to cost him dearly. And his undoubted
vanity prompted him to have a little volume of his own in that library
to which he could turn occasionally for the retrospection of his own
cleverness. Now, I must investigate this clever telephone system. I
think I have the clue necessary."

He intrusted the book to Helene for the morning, promising to return
in an hour or two with new information, drolly refusing to tell her his
destination.

"You're a bad, bold boy, and should be spanked, for not letting some
one know where to look for you in case you get into difficulties," she
pouted. "Perhaps I will do some equally foolish thing myself."

"If you knew how you frightened me yesterday!" he began.

"Did you really worry and really care?" But Shirley had slipped out of
the door, leaving her to wonder, and then begin that long delayed letter
to Jack.

CHAPTER XIX. AN EXPEDITION UNDERGROUND

The criminologist picked his way through the swarming vehicles which
swung up and down Broadway, across to Seventh Avenue, where he turned
into a plumber's shop. This fellow had han