Ghoulfire - The Reflected City, #2

A ghoul is at large. A Guardian is dead. Trouble has come to Lumen. Trey Shield is frustrated and on edge. Aided by the shadowy figure known as the Master, the ghoul has eluded him and the Bureau for months. Then it murders a Guardian, one of the twelve magicians who protect Vaeland, and Trey has to answer to the authorities for his failure. Meanwhile, Arabella Trent can no longer ignore the after-effects of her disembodiment.
Called into the service of a warrior saint, she finds herself suddenly charged with bearing the Arcana, a centuries-old magical artifact with a mind of its own. Her sudden elevation has attracted the ghoul's notice. Trey never wanted to involve Arabella in danger-but it's come for her anyway.