During the Hyborean Age, a group of sorcerers from Acheron created a mask from the skulls of dead kings and sacrificed their pure-blooded daughters to the dark gods in order to give the mask the power to subjugate the entire world.
After killing countless people in their campaign to conquer the planet, the sorcerers were defeated by the Cimmerians led by Corin (Ron Perlman), who destroys the mask, scattering the pieces across the land, and keeping one for himself. Years later, the Cimmerians are at war with a rival clan.
Corin's pregnant wife is fatally injured in the battle, but is able to give birth to a son, Conan, before succumbing to her injuries. Conan's birth on a battlefield, and subsequent survival, is considered to be a powerful omen.
As an adolescent, Conan (Leo Howard) becomes a fierce, but unfocused, warrior. After a young Conan returns from a warrior's trial with the severed heads of members of a savage tribe, Corin takes the boy to his foundry and teaches him the Riddle of Steel.
Conan insists that he is ready to wield his own sword, but Corin reminds him that once a blade has been forged, it must still be tempered with ice before it can be wielded.
Not long after, village are attacked by armored warriors, sporting a symbol of a large, two headed serpent. The leader, Khalar Zym (Stephen Lang), confronts Corin, demanding his piece of the Mask. When Corin refuses, he is restrained and tortured.
Conan, in an angry moment of defiance, attacks one of the warriors, Lucius (Steven O'Donnell), maiming him when he cuts off the man's nose. After recovering the piece of the mask, Zym has Conan and Corin chained to a pole, a cauldron of molten metal hanging precariously above them, then sets fire to the foundry.
Corin sacrifices himself to enable Conan to escape. Conan is left an orphan and bears wounds on his palms from his attempts to save his father. Conan wanders out and claims a large sword as his own -- his father's sword was stolen by Zym's daughter, Marique.
Twenty years later, Conan (Jason Momoa) is a mercenary, working with a Zamoran pirate named Artus (Nonso Anozie). The two men raid a slave camp and take the survivors to the city of Messantia.
The snake cult has grown in size over the last decade, and they have a small garrison in the city. Conan sees Lucius, now an out-of-shape warden, pursuing a pickpocket, Ela-Shan (Saïd Taghmaoui), and allows himself to be arrested in a bid to learn more about his enemy.
Conan soon escapes prison and tortures Lucius for information about Zym and the snake cult. After Conan promises to spare him, Lucius reveals that Zym is seeking the pure blood descendant of the sorcerers of Acheron, as it will take their blood to unlock the Mask's true power.
Satisfied that he has gotten all he can out of Lucius, Conan leaves him at the mercy of the liberated prisoners, reminding the frightened guard "I only promised I wouldn't kill you."
Ela-Shan tells Conan that, if he ever needs him to return the favor, Conan will find him at Arlagon, the City of Thieves.
Meanwhile, Zym and Marique (Rose McGowan), attack a monastery where they believe the Pureblood is. Sensing something is wrong, the elder priest Fassir (Raad Rawi) instructs one of his students, Tamara Amalia Jorvi-Karashan (Rachel Nichols), to flee to her birthplace, then confronts Zym to buy time for her to escape.