omething that will
surprise you a heap. Are you ready for a shock?"

"Oh; I can brace myself for nearly anything, Peg," replied Frank,
easily; "so suppose you tell us your great news. Have you entered for
the endurance race at the annual cowboy meet next month; or do you
expect to take the medal for riding bucking broncos?"

"Any ordinary range rider might do that, even if he lost out," Peg went
on; "but my game is along different lines; see? I'm on my way right
now to run down the mystery of Thunder Mountain! I understand that for
years it's puzzled the whole country to know what makes that roaring
sound every now and then. Many cowboys couldn't be hired to spend a
single night on that mountain. As for the Indians, they claim it is
the voice of Great Manitou; and steer clear of Thunder Mountain, every
time. Get that, Frank?"

"Well, Peg, you have given me a jolt, for a fact," answered the saddle
boy, as his face expressed his surprise. "I allow that you show a lot
of nerve in laying out such a big plan; and if you only find out what
makes that trembling, roaring sound, you'll get the blessing of many a
range rider who believes all the stories told about Thunder Mountain."

Peg stiffened up in his saddle, as though he realized that he was
engineering a tremendously important thing; and had a right to be
looked up to as a hero, even before the accomplishment of the deed.

"Well, that's always the way with you fellows out here, I find," he
remarked, loftily; "you leave all the big things to be done by fellows
with real backbone. But then, I don't mind; in fact I'm obliged to you
for neglecting your opportunities so long. Just you wait, and you'll
hear something drop. Couldn't I induce you to name a price on that
black beauty, Archer?"

"Domino is not for sale at any price," replied the other, quietly.

"Oh! all right then. So long, Frank. Go back home, and wait till I
send you word about what I've found out!" and with a careless wave of
his arm Peg whirled his horse around, and galloped off.

"Now, I wonder did he mean that; or was he just bluffing?" said Frank,
as he turned to his chum.

"He looked as if he might be in dead earnest," replied Bob; "but you
know him better than I do, and ought to be able to say whether he'd
have the sand to take up such a job as that."

"Oh! nobody doubts his grit, when it comes to that," Frank went on, as
though trying to figure the matter out. "And he seems to wa