The first two sea battles go the way of Athens, with the Persians falling for their traps and losing many more ships. Artemisia, the Persian Fleet Commander, requests the presence of her nemesis so she can talk terms.
She offers Themistocles a high position on her fleet and truce for his men, but he declines. He is sent back, and a woman scorned and all that...
So later she summons her secret weapon - an oil tanker, with slaves on board to pump oil into the sea. They cover the Greek ships, and then send saboteurs into the sea with oil-filled turtle shells on their back. The Greeks destroy the tanker too late before their fleet has been decimated.
One saboteur manages to break through undetected. Artemisia readies her bow, and shoots a flaming arrow into his back. He erupts, bringing destruction to the Greek fleet. Themistocles is knocked unconscious into the water, and washes up on shore.
Nothing stops the Persian advance, and they sack Athens.
Themistocles is not finished. He goes again to Sparta, where he finds Queen Gorgo mourning the death of her husband. She refuses to help Athens, but he appeals to her sense of justice.
Themistocles gathers his fleet for one last showdown. Using the hunchback traitor, he returns a message to Xerxes. Artemisia cannot resist the temptation to finish off her enemy, and defies Xerxes to take the whole Persian fleet to finish off the remaining few Athenian ships.
As the two forces draw together, Themistocles readies his ship - then when they collide he races up to the top deck on a horse, and gallops across the Persian ships, jumping from one to the next, to get to Artemisia. She is pretty nifty with a sword, and with her bodyguard troop of Immortals the Greeks are no match for her ...
Until Themistocles gets closer, proving that he has impossibly superior sword skills than anyone in the known world, and easily slices through any Immortal soldier. She manages to cut him, but he defeats her - and leaves her to look on the approaching Greek fleet led by Queen Gorga. She cannot take it, fights back, and he has no choice but to drive his sword through her.
Xerxes turns his back, as the Greek ships crash into his Persian fleet.