Conan is at the pinnacle of his career in this story, having roamed the imaginary prehistoric world of Hyborea and, with native cunning and sheer force, fought his way to the throne of Aquilonia. He is the archetype of the invincible warrior: tough, fearless and incredibly strong.

As the novel opens, King Conan is captured by the magic of the evil sorcerer Xaltotun, whom Conan's enemies have raised from the dead, after three thousand years, for the express purpose of removing Conan from the throne. Conan's armies are so unprepared to battle Xaltotun's sorcery that they are routed on the battlefield and Aquilonia is conquered.

Conan is secretly released from prison by a slave girl who loves him, and he fights his way out of the dungeon catacombs to freedom, defeating a giant murderous ape who blocks his way. In the course of his escape, he overhears a secret meeting and learns that the source of Xaltotun's power is a mysterious jewel, the Heart of Ahriman, which Xaltotun's allies have stolen from him to insure their control over him.

Conan resolves to track the jewel across the barbaric landscape of Hyboria, destroy Xaltotun and regain his kingdom.