Eff was born a thirteenth child. Her twin brother, Lan, is the seventh son of a seventh son. This means he's supposed to possess amazing talent - and she's supposed to bring doom to everyone around her. Undeterred, her family moves to the frontier, where her father will be a professor of magic at a school perilously close to the magical divide that protects settlers from the beasts of the wilderness. Eff and Lan do not know what awaits them in such an unknown place. There are steam dragons that hover in the sky, and strange creatures that could undermine the homesteaders' very existence. Eff is allowed to learn magic with the other students - but there's always the threat of it going horribly wrong. As a thirteenth child, Eff always feels one short step away from complete ruin. As Eff and Lan grow older, they face challenges they never could have dreamed of. And then their magic is put to the test in a standoff that will alter their lives forever.