Chuck Bennett discovers from an old family bible that many years ago a man from Missouri cached his diamonds somewhere in the area of Carlsbad Caverns in New Mexico. When news gets out about the discovery, so-called descendants of the man are eager to question Chuck and his friend and make off with the loot. The boys manage to foil all of these would-be heirs and ultimately put their discovery to good use.
The recurrent themes of the books in the Wilderness Mystery Series are natural phenomena—caves, canyons, mountains, sand dunes, and forests—and a sense of the past as seen through archaeology. In many of the narratives, events of long ago are seen to have left traces of their passing. Notwithstanding the fact that the books were written in the 1950s, the progressive Franklin Folsom (alias Troy Nesbit) had refreshing views of women, Native Americans, and the environment, and he was prescient in having his characters often oppose corporate and government efforts to develop wilderness areas.