m now it would
mean the letting loose of a destructive flood."

"But who would want to blow up the dam?" asked Blake.

"Enemies of the United States," was the captain's answer. "I don't
know who they are, nor why they should be our enemies, but you
know several nations are jealous of Uncle Sam, that he possesses
such a vitally strategic waterway as the Panama Canal.

"But we don't need to discuss all that now. The point is that we
are going to try to prevent this thing and we want you boys to
help."

"With a flashlight?" asked Blake, wondering whether the captain
depended on scaring those who would dare to plant a charge of
dynamite near the great dam.

"With a flashlight, or, rather, with a series of them, and your
moving picture cameras," the captain went on. "We want you boys to
get photographic views of those who will try to destroy the dam,
so that we will have indisputable evidence against them. Will you
do it?"

"Of course we will!" cried Blake. "Only how can it be done? We
don't know where the attempt will be made, nor when, and
flashlight powder doesn't burn very long, you know."

"Yes, I know all that," the captain answered. "And we have made a
plan. We have a pretty good idea where the attempt will be
made--near the spillway, and as to the time, we can only guess at
that.

"But it will be some time to-night, almost certainly, and we will
have a sufficient guard to prevent it. Some one of this guard can
give you boys warning, and you can do the rest--with your
cameras."

"Yes, I suppose so," agreed Blake.

"It will be something like taking the pictures of the wild animals
in the jungle," Joe said. "We did some of them by flashlight, you
remember, Blake."

"Yes, so we did. And I brought the apparatus with us, though we
haven't used it this trip. Now let's get down to business. But
we'll need help in this, Joe. I wonder where Alcando--?"

"You don't need him," declared the captain.

"Why not?" asked Joe. "He knows enough about the cameras now,
and--"

"He's a foreigner--a Spaniard," objected the captain.

"I see," spoke Blake. "You don't want it to go any farther than
can be helped."

"No," agreed the captain.

"But how did you and the other officials hear all this?" Joe
wanted to know.

"In a dozen different ways," was the answer. "Rumors came to us,
we traced them, and got--more rumors. There has been some
disaffection among the foreign laborers. Men with fancied, but not
real grie