"Call up Wonderleigh's place; he's sure to be there at this hour, playing pinochle in the back room. The number's 35-79 Parkside."
In a few moments the secret agent had Mr. Jackson on the wire.
"I want to speak to you about Karkowsky, lately on your route," said he.
There was a laugh at the other end; then the postman answered:
"This ain't the police?"
"Not exactly, but something of the sort."
"Well, I've kind of expected that somebody would ask me about that old scout; they seem to have asked everybody else."
"Would you mind telling me about the trouble you had with him regarding some letters?"
"Oh, that! Sure. You see, Karkowsky for the first while that he lived at Brekling's place received a letter a couple of times a week that always got my attention. It was in a woman's writing—kind of a foreign writing that was mighty hard to make out. It was always a brown, square envelope, and it was always post-marked at Central Station. I couldn't tell you all this about most of the letters I handle, but this one gave me so much trouble at first finding out what the address was that I knew it by heart.
"One day I handed one of them to Karkowsky, and he threw it back at me.