In the Kingdom of Five Cities, known as Etholius, four cities are devoted to fire, water, wind, and earth, respectively. The fifth city, Aethrum, is the capital. Grace Athensius lives in Aqualia, making her a water-bender. But her water powers are practically nonexistent. When she manages to pass the national proficiency test, without using water-bending at all, she is alienated from her peers and her family, who claim that she does not belong in Aqualia. Then Grace receives a gift, an elaborate weapon - with an anonymous note warning her that she will need that weapon soon. "Etholius is the Kingdom of Five Cities, but four will fall and a sixth will rise," the note reads. Grace's journey to discover her true powers leads her through the Kingdom of Five Cities and beyond to find the true danger that Etholius faces. And although Grace has never cared much for Aqualia, she does hope that her home city remains safe in the war to come.