In a nuclear plant in Kimberly, workers are nervous when a congressional committee comes for a surprise inspection. A few minor problems come up during the inspection, but the plant continues to run at full capacity--at least at first.
Half-way through the inspection, one of the converters has a major failure. Jorgenson and his team had been trying to use a new isotope in the giant reactors, but the unstable isotope causes disaster to strike. The reactor walls give out, and Jorgenson is stuck inside.
Jorgenson is the only survivor, and the only person who knows how to stop the reactor from causing a disaster that could wipe out half of the continent, but he is stuck inside the reactor with no way to communicate with anyone. It's a race against time to rescue Jorgenson so that he can save the world from nuclear fallout.
The magazine version of Lester del Rey's frightening novel appeared in 1942, long before Three-Mile Island and Chernobyl. Some see this book as a scarily accurate prediction of later nuclear meltdowns. Del Rey was an important science fiction writer and publisher, but none of his work had greater impact than this early novel.