Queen of Rats by Chris R. Sendrowski

Imprisoned in the vast sewer system beneath the jungle city of Nethra, Ember Wellen, a musician of unparalleled talent, has one desire: avenge the murder of her sister. But to do so, she must save the city from the wicked king and stop a long-forgotten nightmare gestating beneath the city streets. Win or lose, no one will survive unscathed, not even the Queen of Rats. Queen of Rats is a dark fantasy novel filled with action and magic set in the same world as Chris R. Sendrowski's other novels, Haliden's Fire and Dregs of the Culver Waste.