The battle of Thermopylai, 480 BC. King Leonidas I of Sparta and his army of 300 stop the advance of an invading Persian army that counts tens of thousands soldiers. In the end, he falls, but not before costing the Persians so dearly that their conquest for Greece fails on the very shore they landed. Two generations later, Alexios and Kassandra were born. Depending on player's selection, one of them plays the protagonist while the other becomes an antagonist. But before they were shaped into mighty warriors, they were children, they were Spartan, and one of them was to be sacrificed to the gods at the behest of the Cult of Kosmos who works in the shadows yet controls the world through chaos. Many years later, the remaining sibling lives on the island of Kephallonia, while the other is presumed dead by being thrown from the mountain in the sacrificial process. The protagonist living in Kephallonia was rescued and raised by Markos, a shady character with a knack of making drachmae and getting himself into trouble, but with a good heart. Being raised by such a person made the protagonist took a path of becoming a mercenary. Feeling ready, it was time to venture into the world and find the answer to many questions that troubled the protagonist from the childhood. Why did their father allow the sacrifice? Is the mother still alive? Who or what is the Cult of Kosmos and what are their plans? Thus, Alexios' or Kassandra's odyssey begins.