"Well, we'll give the matter a fair trial, anyhow." Upon reaching Swamp Angel, they soon located the little hotel and there turned into bed for a few hours' sleep. It was late in the afternoon when they returned to Dalton's. Here they met the old negro again and he said: "Yo's come back too late, gemmen." "How so?" asked Old King Brady, in puzzled tones. "Massa Mason an' Sim done gone an hour ago." "Where to?" "York." The detectives were keenly disappointed. However, they did not complain, and went away to search the swamp again for some trace of the missing body. No success crowned their efforts. In fact, after a useless search, covering a period of three days, they at length gave up the hunt in despair and returned to New York. It was useless to remain prowling around that bleak swamp trying to dig up a mystery that baffled all their ingenuity. "We went beyond our depth," said Harry, when they reached New York. "The game was too hard to solve. The mystery of the murdered man in the box must remain unsolved. It can go on record as one of the many strange cases that have baffled the detectives before. It's our duty now to report the matter to our chief, drop it, and resume our attempt to locate the broker's mail thief." "Then come to headquarters at once," said Old King Brady, as they left the cars. They met the chief in his office and he smiled pleasantly, and asked: "Well, where have you two been keeping yourselves hidden during the past week? I haven't seen or heard from you lately." The Bradys told him what they had been doing. He listened attentively, with a grave look upon his face, while they were giving him the facts, and said when they finished: "Then that murder mystery was too much for you, and you went beyond your depth trying to solve it, eh? Well, it's just as well you let it drop." "Anything new going on?" "Yes. Something relating to your mail robbery case." "Indeed! What was it?" "Oliver Dalton has disappeared." "Where to?" "Nobody seems to know." "That is very strange." "You had better go up to his house and get the particulars from his daughter. She is frantic to find her father. Some points might be gained in the broker's Broad street office." "We'll follow your advice, sir," said Old King Brady. The chief did not seem to have many facts in relation to the case, so the detectives finally left him. Going to the broker's office, they found it occupied by half a dozen clerks. Having asked for Mr. Dalton, the office boy said to them: "You'd better see Mr. Mason about that matter, sir." "Is the broker's nephew in?" asked Harry. "Yes. He's the boss here now. Got your card?" Harry handed him a business card and he carried it into a private office in the rear. A few minutes later he came out, with a smile on his face, and said to the detectives: "Mr. Mason says for you to come in."