Black Key: Dragon Key Book 5 (Dragon Shifter Romance) - Dragon Key, #5

Adventure calls again to Kate and Tegan, but this time the stakes are higher as they put their souls on the line to protect each other from a growing darkness. Their trouble begins with a cry from Zahn, the mysterious Blood Wizard with whom they have a contract. The call is cut off mid-sentence, however, and their intention to find out the truth is vetoed by Domini, their employer and the owner of their other blood contract. Their curiosity, however, won't be satisfied until they find out what's happened to the ancient and powerful vampire.
They follow a trail of intrigue and betrayal that leads them north into the domain of the humans where Domini rules with whispered threats and sweet promises of power. There they find their allegiances are tested and their lives hang in the balance as together they attempt to foil the dark plots of their many foes before they fall to the shadows.