Synopsis from Goodreads

Worlds divide, magic slays, and love lies in the second book of Josephine Angelini’s The Worldwalker Trilogy. "You think I’m a monster, but my choices, as ruthless as they seem, are justified." Lily is back in her own universe, and she's ready to start a new life with Rowan by her side. True, she almost died in the Pyre that fueled their escape from New Salem, and must hide her magic for the safety of everyone she cares about, but compared to fighting the Woven, the monstrous creatures inhabiting the alternate Salem, life is looking pretty good. Unfortunately, Lillian, ruthless ruler of the 13 Cities, is not willing to let Lily go that easily. If she can’t persuade Lily to return to her world, she will force her to come back by doing away with the ones she loves. Picking up right where Trial By Fire left off, Firewalker is another sexy, fast-paced, heartbreaking thrill ride from internationally bestselling author Josephine Angelini!