The battle that changed the course of Western civilization...
When Riley's time machine transports her to ancient Sparta, she meets the Greek general Leonidas, who is preparing to resist the Persian army of Xerxes in the mountain pass of Thermopylae. Aware of the much larger size of Xerxes' army, Riley tries to convince Leonidas to alter his strategy in order to avoid a certain rout.
When Leonidas refuses to concede, Riley uses her knowledge of modern warfare to help the Greek army bolster their defenses and fight off the invading Persians. But the battle takes another turn when the Persian navy penetrates the Greek defenses in the Straits of Artemisium.
With Riley taking an increasingly prominent role in the military planning, before long she and Leonidas develop a torrid romance. Fearful of history's fate on the outcome of Leonidas's campaign, she must make a difficult decision whether to alter the course of human history...