"I wish you to go to the post office for me," said the man, as soon as he entered. "Go to the general delivery window and ask for letters for Samuel Barrows. That is my sick brother-in-law who is visiting me from Michigan." "Yes, sir." "Of course you know where the post office is?" "Oh, yes. I've been past there several times." "You needn't be in a hurry. Wait until they sort the eleven-o'clock mail." "Yes, sir." The distance to the post office was a considerable one. But Nat was a good walker, and found it was only half-past nine when he got there. To while away the time he determined to walk out on the Brooklyn Bridge and take in the sights from that elevated structure. Making his way through the crowd on Park Row, he was soon out on the bridge, and walking in the direction of Brooklyn. There was a stiff breeze blowing, and several times his hat was almost lifted from his head. Suddenly he heard a shout, and saw a stout man running wildly after some papers which the wind was carrying along the walk on the bridge. The man secured one of the papers, but two others were fast blowing beyond his reach, when Nat rushed up and secured them just as they were on the point of being carried into the river. "Have--you--got them?" puffed the man, as Nat came towards him. "Yes, sir. Here you are," and Nat held out the papers. "Good! I was afraid they were lost to me!" And the stranger heaved a heavy sigh of relief. "Were they valuable?" asked our hero, curiously. "Quite so. They are the legal documents in an important real estate case now before the courts. It was very kind of you to pick them up for me." "Oh, it wasn't so much to do," answered Nat. "Nevertheless, I am much obliged," added the stout man, warmly. "I shouldn't have come out on the bridge with them. But I love to get the breeze. I think it does me good. Much obliged;" and then he passed on. "I guess he's a lawyer, or a real estate dealer," thought Nat. "Well, he ought to walk. It may take some of the fat off of him." Nat walked half-way to Brooklyn, and then back again. Shortly after eleven o'clock he presented himself at the proper window of the post office. "Has the eleven o'clock mail been sorted yet?" he asked. "Certainly." "Have you any letters for Samuel Barrows?" The clerk looked through one of the boxes beside him. "Nothing," he answered, briefly. "Nothing at all?" The post office clerk shook his head. Seeing this Nat walked away, and started back for the office. He did not suspect that his employer had sent him to the post office merely to get him out of the office, yet such was the fact. Hamilton Dart had no brother-in-law named Samuel Barrows. As a matter of fact, Hamilton Dart--that was not his real name, but let us use it for the present, nevertheless--was nothing but a swindler. He was worth only a few hundred dollars, and his brokerage and commission business was such in name only.