A resourceful young inventor and his mechanical Steam Man organize an expedition after receiving word that a college friend has disappeared in Central American jungles; a millionaire father offers a reward and a correspondent also describes a ruined temple filled with treasure and giant anacondas. The narrative follows the preparations, the inventor’s household servants joining him, and the voyage into swamp and forest, describing dangers from reptiles, natives, and terrain, and centers on attempts to rescue the missing man and recover the guarded hoard using unusual steam-powered machinery.