d Wilson, he had started for the
Mexican country without waiting for the departure of the professor's
expedition. A short time later, "Professor Wintergreen's Haunted
Mesans," as the boys insisted on calling themselves, had likewise
started on their quest. With them, at Jack Merrill's invitation, went
Walter Phelps, the son of a ranching neighbor of Mr. Merrill. Walt, it
will be recalled, had shared the perils and adventures of the boys
across the border, as related in the previous volume, and had been the
instrument of piloting them out of the mysterious valley in which Black
Ramon kept his plundered herds.

Mr. Merrill's last words had been ones of caution.

"Remember, boys, that if this trouble in Mexico attains real
proportions, life and property along the border may be in great danger.
In such a case, it will be your immediate duty to turn back."

"But, Dad," Jack had said, "you don't expect that plundering
insurrectos would have the audacity to come northward into the Playas?"

Mr. Merrill laughed.

"I didn't say there was any danger even here, my boy. Least of all,
out in that barren country. If there is an insurrection, it will
doubtless be put down without any trouble, but it is always well to be
prepared."

Like his brother ranchers along the border, Mr. Merrill at that time
had no idea of the seriousness or extent of the insurrection. Had he
had, he would, of course, have prohibited the party leaving the ranch.
As it was, he, in common with his neighbors, deemed the insurrection
simply one of those little outbreaks that occur every now and again in
Mexico, and which hitherto had been promptly squashed by Diaz's army.
And so, with no real misgivings, the party had bidden the bluff,
good-natured rancher good-by, little dreaming under what circumstances
they were to meet again.

But all this time we have been allowing our party to travel on without
bestowing any attention upon them. As the afternoon wore on, Coyote
Pete began to feel real apprehension about reaching their destination
that evening. Walt Phelps' fear about the water had been verified.
The supply was getting low. Provided they could "pick up" the mesa
they were in search of before sundown, however, this was not so serious
a matter as might have been supposed. Coyote Peter knew that there was
a well at the mesa, the handiwork of the ancient desert-dwellers.

The really serious thing was, that although they had apparently been
tra