After winning the Civil War against the Confederate Wielders, the Union Machinists have outlawed magic to usher in a new age of steam-powered technology. Diah, an alchemist and the only non-wielder in his family, owes his brother for saving his life in the war; so when Cager is blackmailed into procuring the magical hide of the White Buffalo, Diah accompanies him to the Dakota territory.
Their guide is Oni, a half-Lakota woman with plenty of secrets to hide. She's a magic wielder with an illegal wand concealed in her knife - and she's a coyote shifter. To her people, killing the White Buffalo is not only sacrilege, it's dangerous. Oni has no intention of helping them actually achieve their mission - until she falls in love with Diah.