e 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."

He ushered the Bradys into the private office and they there beheld
Ronald Mason, the broker's nephew, sitting at his desk.

About thirty years of age, his tall, thin figure clad in stylish
clothing, Ronald Mason was a