In a quiet room on the planet Venus, Princess Quanna sits in front of a mirror and combs her hair. She stares at the mirror’s reflection of the windows behind her, which offer a view of the mountains which separate the city of Darva from the rest of the world. James Douglas, the commander of the last Venusian Terrestrial Patrol, comes into her room and asks her to grab him a drink. Quanna is a native Venusian while James Douglas is on a mission from his home country of Scotland on Earth. She pours him several drinks and begins to play music on her harp.

James reveals to Quanna that their patrol will be leaving soon, meaning that Earth’s 300-year imperialistic control over Venus will be relaxed. When James falls asleep, Quanna grabs a pistol and rides off to a waterfall cave on horseback where she had been born. A two-hour climb up a mountain, Quanna and her horse embark on a perilous journey to the cave where they are greeted by a group of Venutian royals waiting by a fire and her brother, Vastari. She tells Vastari and the rest of the group about the news James gave her. Ghej, a hooded Martian, remembered how Earth had previously conquered Mars. When one of the members suggests she kill James she refuses and says she has things she wants to learn about him first.

After some quarreling among the group, Vastari tells Quanna to return to James and learn more about their plans. She returns to James and he wakes up to recount a troubling dream he had where he was impaled and killed in the mountains. They are interrupted by a lieutenant who comes knocking at the door. After Quanna leaves the room, the man tells James that Vastari was spotted in the mountains last night and they speculate about a planned attack on the Earthmen before they leave. Ghej comes into the room next and James welcomes him and they talk about how Vastari will eradicate all signs of Earth after they depart and return the planet to how it used to be.

That night, Quanna puts James to sleep with a heavy dosage of medicine and waits for an assassin to come. She discovers that it is Ysitri, one of the royal men from the cave, and she tells him to leave James alone. When he doubts her loyalty to native Venusians, she tells him she’ll lead James into a trap in the mangrove forest tomorrow for Ysitri to kill him. Quanna leads James into the forest, kisses him and then leaves, saying that she’ll be back in five minutes with a surprise. On her way out, she smiles at the hiding Ysitri. As she watches Ysitri raise his dagger towards James, she starts to run in the direction back in their direction and stabs Ysitri herself. In exchange for saving his life, Quanna asks to return to earth with James, to which he refuses. 

As the earthmen depart, they are attacked by the Venusians who steal one of their weapons. The men continue on their journey to the spaceport and Quanna comes to tell James that she has made Vastari promise not to harm him — a promise James doesn’t believe he will keep. Quanna chooses to sabotage Vastari and aid the Earthmen in their escape, leaving the Venusian army powerless against the foreigners. Quanna meets up with Ghej and when James comes back from battle with wounds from arrows, Quanna wraps his cuts.

Ghej takes James to Vastari’s hideout where the Earthman plans to kill the Venusian leader. When they get to the cave, Ghej turns a gun on James and Vastari goes to grab the gun and in the process is struck by Ghej. Ghej reveals that barbarians recently took a Venusian town nearby and that they will soon invade Darva. Quanna grabs the weapon and stands outside of the cave and threatens to blow them all up if they won’t send Vastari out for her to kill. Instead, James steps out and she strikes him. Vastari pledges his life to both James and Ghej for saving his and the three men plan how they will counter the barbarian attacks. 

James takes Quanna with him in his ship and they travel to earth where they plan to distract the barbarians and hold them off of their Venus conquest until Vastari is ready to handle them.