The old gods have fled, and the monsters they had kept at bay for centuries now threaten to drown the city of Valentine, hunting mankind as in ancient times. In the midst of the chaos, a serial killer has begun ritually sacrificing victims, their bodies strewn throughout the city. Lilac Antonis wants to stop the impending destruction of her city by summoning her mother, a blood god—even if she has to slit a few throats to do it. But evading her lover Arcadia and her friends means sneaking, lying, and even spilling the blood of people she loves. Alex and Cecil of Ace Investigations have been tasked with hunting down the killer, but as they close in—not knowing they're hunting their close friend Lilac—the detectives realize the gods may not have left willingly. As flooding drags the city into the jaws of sea demons and Arcadia and her evacuation team struggle to save people, Lilac's ritual killings at last bear fruit—only to reveal her as a small piece in a larger plan. The gods' protection costs far more than anyone has ever known, and Alex and Cecil are running out of time to discover the true culprit behind the gods' disappearance before an ancient divine murder plot destroys them all.