"Yes, whom do they belong to?" demanded Mollie. "If you mean the men we
saw in the boat, I should say they didn't have any more right to them
than we have. They were pirates if ever I saw any."

"Well, you never saw any pirates," remarked Betty, calmly. "But of
course the men in the boat may have hidden the diamonds there."

"Do you think they knew they were in the box?" asked Amy.

"Well, whoever hid the box must have known it contained something of
value," Betty declared. "They would hardly hide an empty box, and if
they had found it locked they would have opened it to make sure there
was nothing of value in it. Of course those men may only have been
acting for others."

"But what are we to do?" asked Amy.

"We must try to find out to whom these diamonds belong," Betty said.
"We'll have to watch the advertisements in the paper, and if we see none
we'll advertise for ourselves. That's the law, I believe," and she
looked at Allen.

"Yes, the finder of property must make all reasonable efforts to locate
the owner," he said, "though of course he could claim compensation for
such effort. I think the papers are our best chance for finding clues."

"Has there been a big diamond robbery lately?" asked Mollie.

"What has that to do with it?" Will wanted to know.

"Because I think these diamonds are the proceeds of some robbery," went
on the girl. "As you say, the stones are wrapped in a paper just as
though they had come from a jewelry store. It might be that those men
broke into a store, took the diamonds and hid them in this secret part
of the box, which one of them owned. They are probably from some big
robbery in New York, or Boston, seeing we're nearer Boston than we are
New York, up here."

"I don't remember any such robbery lately," Roy said, and he was a
faithful reader of the newspapers. "But of course we've been pretty busy
lately. I'll get some back numbers of the papers."

"Ha! What's going on now?" asked the voice of Mr. Nelson. He had come in
from the station, having run up to Boston on business.

"Oh, Daddy!" cried Betty. "Such news! You'll never guess!"

"You've solved the cipher!" he hazarded.

"No. We didn't need to. We solved the mystery of the box, and look----"

She spread the sparkling stones out before him.

"Whew!" he whistled. "I should say that _was_ news. Where did you get
those?"

"In a hidden compartment of the black box. I stumbled on the secret
spring by accident when I was me