t one?" asked Mollie. "Oh, isn't this fascinating,
girls!"

"It will be more fascinating to discover the secret," Betty said.

"I don't know what letter is next in importance, or, rather frequency,"
Allen answered. "But we will each take a book and by counting the
letters on a page we can find out."

"Some work!" groaned Roy. But they began it. Even Mr. and Mrs. Nelson
were interested enough in the novel game to attempt it.

It took some little time, but at last Betty and Allen, who were working
together, announced that they found A to be the next most predominating
letter after E. And the others' search agreed with this. Then in order
came o, i, d, h, n, and so on.

But they did not do that in one day, or even two, for they found it
rather tiring to the eyes. So that it was not until three days after
the finding of the box that Allen was ready with the ground-work of his
cipher translation.

In the meanwhile the motor boat had been repaired and was ready for
service. The weather had cleared, and in the intervals of working over
the mysterious paper in the box the boys, escorted by the girls, went to
the place where it had been found. The hole in the sand was just as they
had left it.

"The men haven't come back to discover their loss," said Betty.

"Or, if they have, they are leaving the ground undisturbed with a view
to getting a clue to the one who took the box," Allen said, with a look
at Betty.

The next day a real attempt was made to decipher the code. As Allen had
said, it was made up of several letters, numbers and arbitrary signs,
some of them resembling Chinese characters in form.

"The thing to do," said Allen, "is to pick out the letter, number or
sign that occurs most frequently. In other words, the predominating one.
And that will be E, for E is the predominating letter in any
communication. Now we'll begin."

They all had great hopes, but, alas! they were doomed to disappointment.
For either Allen's system was wrong, or else the cipher did not follow
the plan of any of the well known ones. They succeeded in deciphering
it, after a fashion, but the result was a meaningless jumble of words
that told them nothing. The word "treasure" did not even occur; that is,
according to the translation made by Allen.

"Well, I give up," he said, with a sigh of disappointment. "I sure
thought I could make something of it, but I can't."

"Maybe Will could send it to some of his Secret Service friends,"
su