This Savage Song

Kate Harker and August Flynn's families rule opposite ends of Verity, a grisly
metropolis where violent acts summon real monsters: bloodsucking Malchai; clawing
Corsai; and soul-stealing Sunai. The truce that keeps the families at peace is
crumbling, and August is sent to spy on Kate. But when Harker's men try to kill her
and pin it on the Flynns, August and Kate find themselves running from both sides,
in a city where monsters are real...