After the events of Mary of the Aether and Mary of Shadows, Mary Lanham is on the run, desperate to stay one step ahead of the terrible Devourers who pursue her by the dark of night. She flees through lonely places, following country roads, passing through tiny towns and trying to stay out of the public eye. Meanwhile, back in Chesset, her friends find themselves under attack by Lookers who want to use them as bait to draw Mary home. A trap is sprung, and the whole world watches as universes collide in an explosive showdown that will change everything.