As the Persian Empire continues its conquest of Greece, Athenian general Themistocles seeks to unite the Greek city-states against the invasion. Standing in his way are the armies of King Xerxes and the formidable Artemisia, commander of the Persian fleet, driven by a deep desire for revenge. While the Spartans confront the enemy at Thermopylae, Themistocles leads his forces into fierce naval battles that will determine the future of Greece.