This is book number 2 in the Kingdom of Xia series.
Skybright is plunged into the terrifying Underworld where demons are bred, while Stone, stripped of his immortal status, must find a way to close hell's breach before more mortals die. Meanwhile, Zhen Ni, Skybright's former mistress and friend, is now wed to the strange and brutish Master Bei, and she finds herself trapped inside an opulent but empty manor. When she discovers half-eaten corpses beneath the estate, Zhen Ni worries that Master Bei is not all he seems. As Skybright begins the dangerous work of freeing Zhen Ni with the aid of Kai Sen and Stone, nothing can prepare them for an encounter so dark that it threatens to overtake their very beings.