When Sal is named Successor to Mother Morevna, a powerful witch and leader of Elysium, she jumps at the chance to prove herself to the town. Though long plagued by false visions of rain, Sal knows she's a leader. Even the arrival of Asa, a human-obsessed demon in disguise, doesn't shake her confidence in her ability-- until a terrible mistake results in both Sal and Asa's exile into the Desert of Dust and Steel. They join a gang of girls headed by Elysium exile and witch Olivia Rosales. Together they create a cavalry of magic powered, scrap metal horses to save Elysium from the coming apocalypse.