Patricia C. Wrede

Eighteen-year-old Eff must finally get over believing she is bad luck and accept that her special training in Aphrikan magic, and being the twin of the seventh son of a seventh son, give her extraordinary power to combat magical creatures that threaten settlements on the western frontier.

Eff learns about magic and ways of looking at the world when she embarks on a government expedition with her twin brother, her best friend, and her mentors Professor Torgeson, Wash Morris, and Professor Ochiba.