h."

"Go on!" laughed Henry Blackford. "You'll be saying next that it's
smugglers' booty, and you'll be asking us to pay a duty on it. Let's
open the box and see what it is--maybe nothing but seaweed. I've heard
of jokes being played before," and he looked at the girls meaningly.

"Oh, _we_ didn't hide it and then find it again," Amy assured him, so
earnestly that the others laughed.

"Well, here goes for a try, anyhow," said Mr. Nelson.

With a bunch of assorted keys he tried one after another in the strange
lock. Some keys would not even enter the aperture, while others turned
uselessly around in it.

Betty's father used all he had without success, and then the boys were
called on. They were not able to produce the Sesame to the japanned box,
and Will's plan of using an axe was finding more favor when Allen
produced a small key of peculiar make.

"Try this," he said. "It locks the switch on the motor boat, but it may
fit. It looks as though it would."

And, to the surprise of them all, it did. As though it had been made for
that lock, the little switch key slipped in. There was a click, a
grinding sound, as the cover slipped on the sand-encrusted hinges, and
the lid went back.

"Stung!" cried Roy, as nothing was seen but a slip of paper within the
black interior.

Mr. Nelson lifted it out.

"I can't make anything of this," he said. "It's some sort of a note,
written in cipher, I should judge. It is signed 'B. B. B.'"

"The same letters that are on top of the box," said Allen.

"Was there ever a pirate who had those initials?" asked Mollie, and the
others laughed. "Well, there might have been," she went on. "I don't
think it's so funny."

"Of course it isn't, dear," declared Betty. "I guess we're all a bit
nervous. Is that all there is, Daddy?"

"Everything, my dear. The box is empty save for this bit of paper that
doesn't make any sense."

"We must translate that at once, sir," said Allen. "If it is in cipher
that's all the more evidence that it means something. I might have a try
at that secret message, or whatever it is."

"Well, you're welcome to have a go at it," assented Mr. Nelson. "It may
all be a joke, so don't take it too seriously."

"I'll not," agreed Allen.

He took the paper from Mr. Nelson's hand. The others looked over his
shoulder at it.

"Oh, what do you suppose it means?" marveled Grace. "Do hurry and
translate it, Allen."

CHAPTER XII

THE FALSE BOTTOM

For a m