“If the letter was from Mr. Potter, and it wasn’t the millionaire who mailed it, he must have got some one to do it,” the chief clerk of the sub-station suggested, and Larry was forced to adopt this idea.  He inquired as to the location of the box at which the carrier stood when he received the missive, and asked in what direction the man came from.  Having learned these facts, and deciding he could gain nothing more by staying longer at the sub-station, Larry hurried to the Leader office.

“Well, I’ve gained something,” he said to himself.  “I’ve got a good story, and I have a slender clue to work on.  I must write the story first, however.  Then I’ll go back and tell Grace what I learned.”

The account of the letter and the circumstances under which it was mailed created a new sensation in the Potter mystery, and, as on several other occasions, the Leader scored a beat.

As soon as he had finished the story Larry went to see Grace, whom he found anxiously waiting for him.  She asked a score of questions as to what he had learned, and the reporter told her all about his trip to the sub-station.

“What are you going to do next?” she inquired.

“I think I’ll go over on the East Side and make some inquiries.  Your father may be staying there,” answered Larry.

Going downtown in an elevated train, and taking a stroll through that populous section, known as the “East Side,” Larry soon found himself in the neighborhood of the box at which the carrier had received the letter written by Mr. Potter.  He took a brief survey of the locality.

“Not very promising,” was his mental comment.

All about were big tenement houses of a substantial kind.  They were built of brick, and from nearly every window a woman’s head protruded, while the street swarmed with children.  It was a neighborhood teeming with life, for it was the abode of the poor, and they were quartered together almost like rabbits in a warren.

For want of something better to do, Larry strolled down one side of the street, at the end of which was located the letter box which formed such a slender clue.  Then he walked up the other side, looking about him idly, in vain hopes of stumbling on something that would put him on the track.

It was late in the afternoon, and the streets were beginning to fill with workers hurrying home, for the day’s labor was over.  As Larry strolled along, rather careless of his steps, he collided with a man in front of a big tenement building.

“Excuse me,” murmured the reporter.

“I beg your pardon,” the man said, grabbing hold of Larry to prevent them both from falling, so forceful had been the impact.  “I was looking to see if my wife was watching for me.  She generally looks out of the window to see me coming down the street, and then she puts the potatoes on.”

“I guess I wasn’t looking where I was going,” said Larry, as he disengaged himself from the man’s grip.  “I was—­why, hello, Mr. Jackson!” he exclaimed.