Conan, alongside his companion Malak, finds himself face-to-face with Queen Taramis of Shadizar, who subjects them to a test of combat against her guards. Impressed by their prowess, she presents Conan with a perilous quest. Initially refusing her proposition, Conan changes his mind upon hearing that she can resurrect his beloved Valeria. Thus, he agrees to escort the Queen's niece, Princess Jehnna, a virgin destined to restore the jeweled horn of the dreaming god Dagoth. To locate the horn, they must first retrieve the powerful magic gem known as the Heart of Ahriman. Joining them is Bombaata, the captain of Taramis's guards, who secretly harbors orders to eliminate Conan once they obtain the gem.
Their journey leads them to the fortress of a wizard where the gem is kept, but first, Conan must rescue his ally Akiro, the Wizard of the Mounds, from cannibals. Along the way, they encounter Zula, a fierce bandit warrior tormented by vengeful villagers. At Jehnna's behest, they liberate Zula, who pledges his allegiance to their quest.
As they venture to the castle of Thoth-Amon, where the coveted gem resides, they camp by a lake. In the dead of night, the wizard transforms into a giant bird and abducts Jehnna. Concerning this, Akiro uses his powers to sense the situation and reveals a concealed entrance to the castle via a water gate. During their frantic search for Jehnna, Conan finds himself isolated from the group, consequently having to battle a fearsome man-beast amidst a hall of mirrors. While initially unable to harm the beast, Conan discovers that shattering the mirrors inflicts damage on it. By demolishing all the mirrors, he exposes the beast as a transformed Thoth-Amon. The wizard’s demise leads to the castle's collapse, prompting a hurried escape for the group. Although they fend off an ambush from Taramis’s guards, Bombaata pretends to know nothing of the attack. Utilizing the gem, they trace the location of the horn.
Later, as night falls, Jehnna confesses her feelings towards Conan, but he firmly redirects her affections, reaffirming his loyalty to Valeria. Their next destination is an ancient temple, where the horn is held. Jehnna retrieves the horn while Akiro translates engravings that unveil a dire prophecy: Jehnna is to be sacrificed in a ritual to revive Dagoth. They are soon confronted by the priests who protect the horn. As they find a hidden exit, Bombaata betrays them, blocking their path and seizing Jehnna. Nevertheless, Conan and his crew manage to escape from the priests and make their way back to Shadizar to rescue Jehnna.
With Malak guiding the way through a secret route to the throne room, Conan finally confronts Bombaata, defeating him in a fierce battle. Zula swiftly deals with the Grand Vizier as he attempts to make Jehnna a sacrifice. As the horn is placed upon Dagoth, he emerges as a monstrous entity, mercilessly dispatching Taramis and challenging Conan. Despite the odds, Zula and Malak join Conan in the battle, but they are effortlessly cast aside by the beast. Akiro reveals to Conan that the horn is the source of Dagoth's vitality, prompting Conan to tear it from the creature's brow before delivering the final blow.
Following their victory, the newly crowned Queen Jehnna extends an invitation to her companions to join her court: Zula is offered the role of captain of the guard, Akiro to become her advisor, and Malak to serve as the court’s jester. In a moment of unexpected romance, Jehnna proposes marriage to Conan, inviting him to rule Shadizar alongside her. However, Conan graciously declines, asserting, "I will have my own kingdom, and my own queen," before departing after a brief kiss. The story concludes with a title card that suggests, "this quest is another story."
