The official novelization of Assassin's Creed Odyssey follows Kassandra, a Spartan-born mercenary cast out and sentenced to death by her own family as a child, as she claws her way back from exile in fifth-century BCE Greece. Her path to becoming a legend takes her through the Peloponnesian War and into the ancient roots of the conflict between Assassins and Templars.
Summary by Loreful, from public sources