When the Twelve Olympians imprisoned the traitorous Titans beneath Mount Tartarus, they lost the Epirus Bow. In 1228 BC, the genocidal king Hyperion searches for the bow to release the Titans. Hyperion captures the virgin oracle Phaedra, to use her dreams and visions to find it.
Theseus is a hoplite trained by the Old Man, who says Theseus has been chosen by the gods. He and his mother Aethra are outcasts due to Theseus being a bastard child. Hyperion attacks Theseus' village. Theseus kills many of his men before being captured and forced to watch as Hyperion murders Aethra.
The Olympians, especially Athena, are sympathetic to the humans suffering at Hyperion's hands, but are forbidden by Zeus to interfere in mortal affairs. Unless the Titans are released, they must have faith in mankind's free will to defeat Hyperion. Zeus himself has trained Theseus in the guise of the Old Man, but reasons he has helped him as a human as opposed to a god.
Theseus is made a slave in a salt mine. Phaedra, held captive nearby, sees a vision of Theseus embracing Hyperion. Phaedra and her sisters attack Hyperion's guards, provoking a riot. She uses the chaos to escape with Theseus and other slaves. They pursue Hyperion, but are overwhelmed by his forces when trying to seize a boat. Poseidon, unseen by Zeus, dives from Olympus into the ocean causing a tidal wave that wipes out Hyperion's men. Afterward, Phaedra sees a vision of Theseus standing near a shrouded body. She takes this to mean that Theseus must return home to bury Aethra.
As Theseus buries his mother in the village's sacred labyrinth, he discovers the Epirus Bow in rock. He frees it, but is attacked by Hyperion's henchman the Beast, whose armour resembles a Minotaur. Theseus kills him and uses the Bow to kill his allies' captors before collapsing from poisoned scratches inflicted by the Beast. Phaedra tends Theseus. Having fallen in love with him, she begs him to take her virginity, stripping her of the visions she deems a curse and they have sex.
They return to Phaedra's temple to kill Hyperion but are lured into an ambush and the bow is seized by Hyperion's hyena. Ares directly intervenes to save Theseus, killing the attackers. Athena then provides them with horses to reach Mount Tartarus. Zeus suddenly descends and kills Ares for disobeying his law, he spares Athena's life because she did not physically interfere like Ares did. Zeus tells Theseus that he and his allies will receive no more aid from the gods as he must justify the faith that Zeus has in him alone.
Theseus warns King Cassander, leader of the Hellenic resistance, of Hyperion's plans to destroy the Hellens and release the Titans, but Cassander dismisses the gods as myth, intending to negotiate peace. Hyperion uses the Bow to breach the city's immense wall, killing many defenders. Theseus rallies the Hellenic army and leads them against Hyperion. Hyperion storms through, kills Cassander, and before Theseus can stop him, uses the Epirus Bow to blast open the mountain and free the Titans. Zeus and the gods descend to battle the Titans, and urge Theseus to fight Hyperion; Zeus destroys the Epirus Bow with Ares' Warhammer. The gods prove more powerful than the Titans, but are overwhelmed, and all are killed except Zeus and a badly wounded Poseidon. As Athena dies, she begs Zeus to not abandon mankind. Hyperion mortally wounds Theseus, but Theseus overpowers and drives a knife into him in an "embrace". Zeus collapses Mount Tartarus on the Titans and Hyperion's men and ascends to Olympus with Athena's body and Theseus.
With time Theseus' story becomes legend. Phaedra gives birth to Theseus' son Acamas. The Old Man tells Acamas that he will fight against evil. Acamas sees the sky filled with Olympians, Titans and Theseus, in battle.
Henry Cavill as Theseus, a mortal chosen by Zeus to fight evil
Stephen Dorff as Stavros, a cunning slave and master thief who joins Theseus on his quest
Luke Evans as Zeus, the God of the Sky and King of the Gods
Isabel Lucas as Athena, the Goddess of Wisdom
Kellan Lutz as Poseidon, the God of the Sea
Joseph Morgan as Lysander, an Athenian soldier who joins King Hyperion
Freida Pinto as Phaedra, a virgin Oracle who guides Theseus on his quest
Daniel Sharman as Ares, the God of War
Peter Stebbings as Helios, general of the Athenian forces
Stephen McHattie as Cassander, the leader of the Athenian Council
Greg Bryk as the monk in service to Phaedra
Alan van Sprang as Dareios, a slave who joins Theseus on his quest
John Hurt as Old Man, a disguise used by Zeus to interact with mortals
Mickey Rourke as King Hyperion, the King of Heraklion (loosely based on King Minos, not the titan Hyperion)
Additional actors include Canadian wrestler Robert Maillet who plays the Beast, Kaniehtiio Horn, Ayisha Issa and Mercedes Leggett as Phaedra's oracle sisters, Corey Sevier as Apollo, Steve Byers as Heracles and Mark Margolis in an uncredited role as the priest of Phaedra's temple.