The story opens with Hernando de Guzman, a Spanish soldier, being ambushed by an Apache warrior. After a tense confrontation, de Guzman kills the Apache with a pistol shot and finds himself lost in the vast plains of the New World. With his horse dead and the camp lost, de Guzman marches aimlessly, driven by the instinct to survive despite the hopelessness of his situation.

As de Guzman continues his journey, he reflects on the futility of the Spanish quest for gold in these desolate lands. His thoughts are interrupted by the sound of a drum, which he decides to follow. The sound leads him to a walled city, unlike any he has seen before, with adobe buildings sheathed in a glazed enamel and intricate designs. The architecture is a blend of Aztec and an unknown, exotic style.

Upon closer inspection, de Guzman witnesses an Apache attack on the city, which is repelled by a strange mist that kills the attackers. He is amazed and horrified by this display of necromancy. As he lies hidden, a girl named Nezahualca discovers him. She reveals herself to be a princess and a slave, degraded from her royal status by Nekht Semerkeht, the city's ruler. She tells de Guzman of her plan to overthrow Nekht Semerkeht and asks for his help, promising to bring him food.

At night, Nezahualca leads de Guzman into the city through a secret gate. They meet an overseer who is in love with Nezahualca and willing to help. However, they are betrayed, and de Guzman finds himself in a chamber where ten men lie dead. He is led by a creature with a woman's hands and a man's hairy arm until he realizes the deception and kills the creature.

De Guzman then finds himself in a throne room where Nezahualca and the young overseer are being tortured. He confronts Nekht Semerkeht, who claims to be an ancient Egyptian magician. De Guzman kills a dragon-like creature about to attack Nezahualca and shoots Nekht Semerkeht, who retreats but continues to live.

Following a fierce sword fight, de Guzman finally defeats Nekht Semerkeht, who falls into a trap door. However, the curse of the magician brings ruin upon the city. Nezahualca tries to resist de Guzman's claim to power, but he overpowers her. In his sleep, he dreams of Nekht Semerkeht warning him of an impending Comanche attack. The Comanches invade, and the city is destroyed. De Guzman dies fighting fiercely.