Two boys explore the rugged terrain of a rural conservation area near their homes. They discover a cave at the bottom of a steep crevice and use it as a secret hideout until becoming trapped by a rock fall. Using the meager resources at their disposal and learning from their environment, they manage to escape after two frightful days in the darkness. The boys learn a great deal about bats, perseverance, and honesty as a result of being trapped and from their experiences after their escape. Their newly acquired knowledge leads the boys into another adventure involving a recluse who helps them escape from dangerous criminals. The boys get away, but soon find themselves again needing help. The recluse, an old man who lives alone in a derelict building that once was a water-powered sawmill, has rigged several devices to discourage unwanted visitors. The boys help capture the criminals with the aid of the old man and his trickery. Although the story takes place in recent times, it touches on life in the olden days. The setting is a collage of real places that coexisted during the 1940's near the author's home in what is now the city of Burlington in Ontario, Canada. An old steam engine, similar in many ways to a machine described in the story, could be found in the village of Kilbride. The sawmill and the icehouse were located a short distance downstream in the hamlet of Dakota. A few minutes walk upstream was a gristmill in Progreston. The sawmill and the gristmill both continued to be operated by waterpower at least into the 1960's. Many features of the two mills have been combined into the fictional home of the recluse in the story. Mount Nemo, part of the Niagara Escarpment, overlooks the village of Lowville which is fictionally portrayed in the story. The cave at the bottom of one of the deep crevices of Mount Nemo is real, as are the almost vertical cliffs that have to be scaled to enter that ethereal other-world. Bats living in the cave are also real; a young boy, unaware of rabies or any other disease so worrisome in this modern world, could harass those docile creatures with no dread of a minor bite.