Black Sphinx of Nebthu

Following the events of "The Witch of the Mists", King Conan of Aquilonia leads a military expedition across Zingara, Argos, and Shem before entering Stygia to confront his arch-enemy, Thoth-Amon. Accompanying him are his son, Prince Conn, Conan's generals Trocero and Pallantides, and Diviatix, a white druid from the Pictish Wilderness, who promises divine support for Conan.

The goal of his expedition is the ancient city of Nebthu, site of a massive sphinx depicting the hyena god of chaos and rumored haunt of Thoth-Amon's Order of the Black Ring. After discovering an entryway inside the sphinx, Conan descends into the depths, reaching a vast chamber where he confronts the massed assembly of wizards.

Thoth-Amon and his fellow sorcerers initially prove themselves to be too powerful for Conan. But Conan had taken the precaution of bringing along a magical jewel known as the Heart of Ahriman (which helped Conan regain his throne in The Hour of the Dragon) With the jewel in his hand, Conan's Pictish ally is more than a match for the Stygians.

Many of the wizards are killed or driven mad by the Heart's powers, but Thoth-Amon manages to unleash the monstrous hyena of chaos against Conan's accomplice. Unfortunately for him, the hell-hound is incapable of fine discrimination. The first army it encounters, and therefore destroys, is that of Stygia. His sanctum in ruins and now persona non grata in his own country, Thoth-Amon is forced to flee, seeking refuge with his last remaining ally - the King of Zembabwei.

Rather than rest content and return to Aquilonia, Conan is determined to settle accounts once and for all and take his army in pursuit to the heart of what would new be called Africa.