Spectyr (A Book of the Order)

Though one of the most powerful Deacons, Sorcha Faris has a tarnished reputation to overcome. She and her partner, Deacon Merrick Chambers, find themselves chasing down rumors of geists, but long for a return to real action. So they jump at the chance to escort a delegation sent to negotiate the terms of the Emperor's engagement. Their destination: the exotic city of Orinthal.
But a string of murders has Orinthal on edge, and Sorcha and Merrick are asked to investigate. Meanwhile the Emperor's sister has unwittingly released a cruel and vengeful goddess, one who it bent on destroying her enemies, including the geistlord who resides inside the shapeshifting rival to the throne--Sorcha's lover....