ggested Grace.

"Yes, I could do that," her brother assented. "Let's let the government
experts take a crack at it, Allen."

"I'm willing," assented the young lawyer.

Betty was in a corner of the big sitting room, the bay window of which
gave a beautiful view of the ocean. She had the queer box in her lap,
and was turning it from side to side, now and then holding it to her ear
and shaking it.

"What are you doing, Betty Nelson?" asked Grace, coming in from a walk
to town.

"I was just listening to see if there was any hidden mechanism in this
box," answered the Little Captain. "I wonder if there's a ruler anywhere
about?" she went on.

She found a foot ruler, and with that began measuring inside and
outside the box, jotting down some figures on a piece of paper.

"What's this--a new way to work out the cipher I couldn't solve?" asked
Allen, coming in.

"Don't talk to me for a minute, please," said Betty, puckering up her
forehead.

She seemed to be adding and subtracting, and then she suddenly cried:

"I thought so! I thought so! It is the only way to account for the
thickness of it."

"The thickness of what?" asked Allen.

"The bottom of that box!" went on Betty. "It has a false bottom. I'm
sure of it. Look here! It is seven inches deep on the outside, and only
five inches deep inside. Where are those two missing inches except in a
false bottom?"

In her excitement Betty tapped on the inside of the bottom of the box
with the ruler, and then a strange thing happened.

There was a clicking, springing sound, and the bottom of the iron box
seemed to rise up in two parts, like the twin doors of a sidewalk
elevator hatchway. The false bottom had been found, and as it swung up
out of the way there was disclosed an opening in which lay a package
wrapped in white tissue paper.

"Oh! Oh!" cried Betty, staring at the box "I--I've found it--the
treasure!"

CHAPTER XIII

THE DIAMOND TREASURE

For a moment the others clustered around Betty like bees in a swarm,
saying not a word. The girls could only gasp their astonishment as they
looked over the Little Captain's shoulder, as she sat there, holding the
black box, the false bottom of which had so unexpectedly opened before
their eyes.

The boys were a little more demonstrative.

"How in the world did you do it, Bet?" asked Will.

"Did you know there was some trick about the box?" demanded Roy.

"She's been holding this back," declared Henry,