t, hidden the
precious stones in her own room, wrapping the box in some sheets of
asbestos, which Allen had left over after putting some on the muffler of
the motor boat.

"The asbestos will protect the diamonds in case of fire," Betty said,
"and I'll protect them in case of thieves. Anyhow, no one, not even the
servants, know where they are, and it would take a good while to find
them in my room."

For she had discovered an ingenious little hiding place for the
mysterious black box.

The boys, after the scare of the men in the cellar, had offered to take
the diamonds up to Boston, or some other city near Ocean View, and put
them in the vault of some bank.

"But you might be robbed on the train, going up," objected Betty. "We'll
keep them here until the secret is discovered. That will be the best
thing to do."

"And that may never be," Allen had said, for he had long since given up
the cipher. Nor had experts, to whom he had submitted it, been able to
furnish a clue to its solution.

So, while the boys had gone out fishing in the motor boat, the girls
prepared for their picnic, leaving the diamonds at home.

Percy Falconer had declined the boys' invitation to go fishing, and when
Betty heard him say that he feared to go out on the water she had looked
at her chums with hopeless despair on her face.

"What if he wants to come on the picnic with us?" she whispered to
Grace.

"We--we'll run away from him!" had been the ultimatum. But Percy did not
pluck up enough courage to trust himself, the only youth, with four
girls.

"I'll go for a run in my car, and may pick you up and bring you back
later," he said, with a glance at his wrist watch. He was still a guest
at Edgemere.

"Well, let's start!" called Betty, and the four girls set off down the
beach.

"Why are you going that way?" asked Grace, as Mollie and Betty, who had
taken the lead, started along a certain path amid the sand dunes.

"Just for fun," answered Betty. "I have a fancy for looking again at the
place where we found the diamonds."

"We can't seem to get rid of them, day or night--sleeping or waking,"
spoke Amy. "Isn't it dreadful how they follow one?"

"Well, I, for one, don't want to get rid of them," Mollie said, with a
laugh. "They are far too pretty and valuable to lose sight of. Though of
course I want whoever owns them to get his property back."

"Even those horrid men?" asked Grace.

"Well, if they have a right to the diamonds,