A group of young border companions and their scholarly guide undertake a hazardous expedition into rugged southwestern canyons and desert, facing wild animals, ambushes, and mysterious warnings. Their journey includes rescues, horse chases, encounters with Mexican rangers, a vanished dwelling, trickery by hostile locals, and deadly traps, as they follow clues into remote mountains. The episodic narrative combines action scenes, frontier hardships, and puzzle-solving as the boys test courage, loyalty, and resourcefulness while uncovering the heart of a long-buried mystery.