The evil Queen Gedren (Sandahl Bergman) leads her army to Red Sonja's house, after attacking them, Gedren attempted to seduce Sonja but because Sonja rejected the Queen's sexual advances and injured her with one of her weapons, she has her entire family killed. Sonja survives being violently raped by Gedren's troops, and even gives Gedren a kind of a souvenir: a brutal scar on the evil queen's face. Later that night, Sonja is visited by a spirit who grants her the strength to seek her revenge.
The story then jumps to a large temple full of white-robed priestesses. They are getting ready to destroy a large, glowing green orb called the Talisman, used by the Creator to forge the world. This dangerous artifact's destructive power increases from exposure to light and the priestesses intend to destroy it before it gets out of control. However, Gedren – now wearing a gold mask to cover her scar – and her aide-de-camp Ikol (Ronald Lacey) attack with their army. The warrior-priestesses resist, but are ultimately subdued by Gedren's forces.
Gedren gets her hands on the Talisman, but not before proving the myth that only women can touch it and survive. Gedren orders the remaining priestesses to be imprisoned in the vault which held the Talisman. One of those priestesses, Varna (Janet Agren), manages to escape. She doesn't get far before she's mortally wounded by an arrow in the back. As luck would have it, she literally falls into the arms of the mighty Lord Kalidor (Arnold Schwarzenegger). She begs him to help find her sister, Red Sonja.
At Castle Berkubane, Gedren places the talisman in a room full of candles to increase its strength. Ikol warns her against this, because too much light will give the Talisman more power than can be controlled, but Gedren ignores his warnings. Back in the castle's main hall, they discover that Sonja and her party are approaching. The queen's wizard shows her Sonja, Tarn and Falkon on a magic screen. Gedren recognizes Sonja and orders that she be brought back to the fortress unharmed. She and Ikol use the Talisman to conjure up a storm, forcing Sonja's band to take shelter in a watery cavern.
Gedren and her Wizard also unleash an "Icthyan Killing Machine" in the cavern. When Sonja and her group try to cross the pond, the monster attacks them. Sonja struggles with the monster, but is unable to find any way to kill it. Kalidor reappears, leaps into the water and wrestles with the beast while Sonja digs out its eyes. They flee with Tarn and Falkon, leaving the metal monstrosity to thrash blindly about the pond.
The Talisman's power is growing too dangerous to control, but still Gedren rejects Ikol's counsel to put it in a darker place. Kalidor, Sonja and Falkon infiltrate Castle Berkubane. To protect Tarn, they convince him to stay behind in order to prevent Gedren from escaping.
Sonja has a final confrontation with Gedren, while Kalidor and Falkon deal with her evil guards in the castle's kitchen/dining hall. Ikol tries to escape with gold looted from Hablock, but is intercepted by Prince Tarn who engages him in combat, finally crushing the evil lieutenant under the castle's rolling stone gate.
Back in Gedren's Chamber of Lights, the Talisman's power breaks the floor open, revealing a hellish chasm of molten lava beneath the castle. Sonja unleashes a brutal barrage of sword swings, which Gedren is barely able to ward off. She finally disarms Gedren, literally shattering her sword into pieces, and runs her through with her own blade, sending the evil ruler plunging to her doom, then casts the talisman in after her. Immediately, the talisman's destruction causes a chain reaction that begins to tear Castle Berkubane apart. The heroes barely manage to escape; Kalidor must hold a couple of pillars on his shoulders while the others pass underneath. Finally, the castle is consumed by the rising volcano beneath it.
Gedren is power hungry and greedy and refused to listen to reason when it came to the Talisman, all of which led to her demise.