As before, all was silence, the drowsy, indistinct voices of the night passing almost without notice.
But Professor Zepplin instead of waiting where he was, reached for his revolver and then strode boldly out into the open space in front of the tents, determined to solve the mystery, and, if possible, without waking the boys.
The reader no doubt already has recognized in the four boys sleeping in the little weather-beaten tents the same lads who some time before had started off for a vacation in the mountains where they hunted the cougar and the bobcat, the thrilling adventures met with on that journey having been related in a former volume entitled, "THE PONY RIDER BOYS IN THE ROCKIES."
They will be remembered, too, as the lads who, in "THE PONY RIDER BOYS IN TEXAS," crossed the plains on a cattle drive, during the course of which Tad Butler bravely saved the life of the Chinese cook, by plunging into a swollen torrent; and later, saved a large part of the great herd, himself being nearly trampled to death in a wild stampede of the cattle.
It will be recalled also, how Tad Butler and his companions, after many strange and startling experiences, solved the veiled riddle of the plains and laid the ghost of the old church of San Miguel, for all time.
The stirring adventures of "THE PONY RIDER BOYS IN MONTANA," too, are still fresh in the minds of those who have followed the fortunes of the four lads since they first started out on their journeyings.
It will be recalled that in the latter story the lads experienced the thrill of being in a real battle between the cowboys and the sheep herders on the free-grass range of the north; how Tad Butler was captured by the Blackfeet Indians, and how, with the help of an Indian maiden, he managed to make his escape.
It will also be remembered that Tad was able to rescue another lad who, like himself, had been taken by the Blackfeet, and to return the boy to his father, none the worse for his exciting experiences. It will be recalled as well, how Tad Butler through his own efforts solved the mystery of the old Custer trail—a mystery that had perplexed and annoyed the ranchers along the historic trail for many months.
And now they were once more in the saddle, having chosen the Ozark Mountains in southwestern Missouri as the scene of their next explorations.
With them they carried a pack train of four mules, these being best adapted to packing the boys' belongings over the rugged mountains. For their guide they had engaged a full-blooded Shawnee Indian named Joe Hawk, known among his people as Eagle-eye, making a party of six, with eight head of stock in all.