unbound the
captives' arms, and stood over them while they ate some coarse food that
was brought into the small cave. They were given coffee to drink, and
then, when the simple meal was over, they were securely bound again,
and left to themselves, while the diamond makers went back to their
machinery.

It was evident that they were going to attempt a big operation, for an
unusually large quantity of the white stuff was prepared. The prisoners
watched them idly. They could see some but not all of the operations. In
this way several hours passed.

Gloom possessed the hearts of Tom and his friends. Not only had their
expedition been almost a failure so far, but the young inventor was
worried lest the gang might discover and wreck his airship. This would
prove a serious loss. Lying there in the semi-darkness the lad imagined
all sorts of unpleasant happenings.

At times he dozed off, as did the others. They had become somewhat used
to the pain caused by the bonds, for their nerves were numb from the
strain and pressure.

Once, as he was lightly sleeping, Tom was awakened by hearing loud
voices in the main cave. He looked out, rolling over slightly to get a
better view. He saw the man who, once before had run in to give news of
an approaching electrical storm.

"Are you fellows all ready?" asked this same man again.

"Yes. Is there another storm coming?"

"Yes, and it's going to be a corker!" was the reply. "It's one of the
worst I've ever seen. It's sweeping right up the valley. It'll be here
in an hour."

"That's good. We need a big flash to make all the material we have
prepared into diamonds. It's the biggest batch we ever tried. I hope it
succeeds, for we're going to leave--" The rest was in so low a tone that
Tom could not catch it.

The storm messenger departed. Folwell and Munson busied themselves about
the machinery. Tom dozed off again, dimly wondering what had become of
Bill Renshaw, and whether the former ghost knew of their plight. The
others were asleep, as the young inventor saw by the dim light of a
lantern in the cave. Then, he too, shut his eyes.

Tom was suddenly awakened by feeling some one's hands moving about his
clothing. At first he thought it was one of the diamond-making gang, who
had sneaked in to rob him. "Here! What are you up to?" exclaimed Tom.

"Quiet!" cautioned a voice. "Are you all here?"

"All of us--yes. But who are you?"

"Easy--keep quiet, Tom Swift! I'm Bill Renshaw!