Lodestar (Keeper of the Lost Cities)

"Sophie Foster is back in the Lost Cities--but the Lost Cities have changed. The threat of war hangs heavy over her glittering world, and the Neverseen are wreaking havoc. The lines between friend and enemy have blurred, and Sophie is unsure whom to trust. But when she's warned that the people she loves most will be the next victims, she knows she has to act. A mysterious symbol could be the key--if only she knew how to translate it"--