"Be at the corner of —— street and —— avenue at eleven o'clock to-night, with a dozen men. You must be in citizens' clothes.
Shadow."
This time I did not hesitate about getting ready to act upon the communication of the mysterious detective.
Promptly at the hour indicated I was at the designated spot, while the required number of men were scattered about in the concealment of various doorways there, and waiting, but out of sight.
I had not long to wait.
It seemed as if Shadow had arisen out of the ground, for I had not seen or heard him approach, yet on turning on feeling my elbow touched, found him at my side.
Holding up his hands between me and the light of the nearest lamp, so that I could plainly see what he was about, he asked me in the deaf and dumb alphabet:
"Can you understand this?"
There are few school-boys who have not at some time learned the art of thus talking with the fingers, and I have once been able to do almost as well as the mutes who are compelled to converse in this way.
Making an effort I found that I could recall the alphabet, and answered:
"I can understand."