Queen Taramis of Khauran awakens one day to find an identical twin sister, Salome, staring her in the face. As an infant, Salome was deemed a witch due to a crescent birthmark on her chest. This birthmark was believed to be a sign of evil, so she was left in the desert to die. However, a magician from Khitai (China) found her, brought her up, and instructed her in the arts of sorcery.

Salome has conspired with Constantius, known as "the Falcon," the Kothic leader of a force of Shemitish mercenaries, to take over the city state. Queen Taramis is taken to the palace dungeon, with the implication of torture and rape. Salome assumes Taramis' identity as queen of Khauran and names Constantius her royal consort. The Khaurani army is disbanded and replaced by Constantius' Shemitish mercenaries, an event which turns violent when the captain of the queen's guard, Conan the Cimmerian, refuses to obey the order.

After putting his back to a wall and killing a number of Constantius' Shemites, Conan is finally captured and crucified for his defiance. Olgerd Vladislav, the Zaporoskan leader of a band of Zuagir desert raiders, rides by with a scouting party and happens by the crucified Conan a mile from the city walls. Vladislav does not entirely help Conan. He has the base of the cross cut, leaving it to fate and Conan's hardiness that he is not crushed by the heavy wood. Vladislav then refuses to give Conan any water, claiming the Cimmerian must wait until after a ten-mile trek to the outlaw camp to prove his worthiness to his band.

In Khauran, Salome's reign as "Taramis" has plunged the state into ruin. Citizens are killed, tortured or sold as slaves; heavy taxes are imposed and women are frequently debauched by the Shemites. Salome desecrates the temple of Ishtar in the center of the city and summons a demon, Thaug, to live within it. Khaurani citizens are routinely sacrificed to Thaug.

Conan has been expanding the numbers of the Zuagirs as Vladislav's lieutenant, while also secretly establishing communication with Khaurani knights who had become refugees. When he has sufficient forces he usurps Vladislav's leadership of the Zuagirs, but does not kill him out of gratitude for Vladislav having saved him from the cross. Conan fakes the construction of siege engines with palm trees and painted silk. Constantius is fooled by this as his scouts cannot get close enough to see them properly and Conan is known to be experienced in all manner of warfare. The mercenary army rides out of the city for an open-field battle with Conan expecting only the lightly armed Zuagirs, but are taken by surprise by Khaurani heavy cavalry hidden amongst them. Conan's forces are victorious.

Meanwhile, Valerius, a former member of the Khaurani army, has discovered the secret of Salome's masquerade, and the fact that Salome is holding the real Taramis in the dungeon. With Conan's forces approaching Khauran, Valerius plans to rescue Taramis and reveal the conspiracy to the people or to escape with the true queen. Conan's victory is not certain to the Khauranis and they are nervous about his intentions if he does take Khauran. When it becomes apparent that Conan has defeated Constantius' Shemites, Salome decides to kill Taramis before Conan can take the city. She thwarts Valerius' rescue attempt and takes Taramis to the former temple of Ishtar to sacrifice her to Thaug. Valerius saves Taramis and kills Salome, but not before she unleashes Thaug. Conan, arriving with his Zuagir forces, who kill the demon with two flights of arrows.

Taramis offers to make Conan councillor as well as captain but he declines, nominating Valerius instead. Conan, as chief of the Zuagirs, mops up the remaining Shemites, capturing Constantius in the process, and leaves to raid the nearby Turanians. Before leaving Khauran, he crucifies Constantius by the stump of the crucifix from which he escaped, commenting with irony to the crucified Constantius the difference between their respective situations: "I hung there on a cross as you are hanging, and I lived, thanks to circumstances and a stamina peculiar to barbarians. But you civilized men are soft; your lives are not nailed to your spines as are ours. Your fortitude consists mainly in inflicting torment, not in enduring it. You will be dead before sundown. And so, Falcon, I leave you to the companionship of another bird of the desert."