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 only bad things to her family and her town. 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 separates settlers from the beasts of the wild.

From New York Times #1 bestselling author Patricia C. Wrede, the second in the series of magic on the western frontier. Eff is riding west, away from the safety of the frontier city she's always known.... Eff could be a powerful magician if she wanted to. Except she's not sure she wants that kind of responsibility. Everyone keeps waiting for her to do something amazing—or to fail in a spectacular way. Worse, her twin brother, Lan, a powerful double seventh son, is jealous of all the attention she's been getting. Even as Eff protests that she's just an ordinary girl, she's asked to travel past the Barrier Spell with one of the new professors at her father's school. The land west of the Barrier is full of dangers, both magical and wild. Eff will need to use all her strength—magical and otherwise—to come safely back home. With wit, magic, and a touch of good pioneer sense, Patricia C. Wrede once again weaves a fantastic tale of the very wild west.

When the government forms an expedition to map the Far West, Eff has the opportunity to travel farther than anyone in the world. With twin Lan, William, Professor Torgeson, Wash, and Professor Ochiba, she finds that nothing on the wild frontier is as they expected. There are strange findings in their research, a long prairie winter spent in too-close quarters, and more new species, magical and otherwise, dangerous and benign, than they ever expected to find. When spring comes, the explorers realize how tenuous life near the Great Barrier Spell must stop a magical flood in a hurry. Eff's unique way of viewing magic has saved the settlers time and again, now all of Columbia is at risk.