In the labs of Los Alamos, after the bombs fell on Japan, one plutonium core remained. The scientists called it "Rufus," but history remembers it as the Demon Core. It was a perfect sphere of death that tolerated no mistakes. Yet, the brilliant physicists played with it, tickling the dragon's tail with nothing but a screwdriver and steady hands. This book chronicles the chilling true stories of Harry Daghlian and Louis Slotin, who both died triggering the core's blue flash of criticality. It is a harrowing examination of scientific hubris, the psychological disconnect between genius and safety, and the invisible, melting destruction of acute radiation sickness. A gripping reminder that the most dangerous weapon is not the bomb itself, but the arrogance of the men who hold it.