Half ancient Greek and half medieval, it tells the stories of three kingdoms on a vaguely Hellenic Mediterranean peninsula. Sometimes warring, sometimes allied, they all face a common threat from a very Ottoman-like empire to the east. Megan Whalen Turner even completely makes up her own pantheon for the mythologies that drive the characters.
The three monarchs and their courts play a continuous but fascinating game of chess with each other, drawn out across the four books. Each one has several brilliant plot twists that had me laughing at myself for not seeing them coming and applauding the author for skillfully weaving a delightful saga.
Recommended the series to Mi Hermana, but also think my nieces and nephews might enjoy it in 4 or 5 years. Time flies!