No rest for the wicked - Kresley Cole

A vampire warrior who yearns for death. . .Three hundred years ago, Sebastian Wroth's brothers forced him to become a vampire-a nightmare in his mind. Shamed and alone for ages, he longs to die. Until an exquisite creature comes to kill him, inadvertently saving him instead. A beautiful assassin dispatched to destroy him. . .When Kaderin the Cold Hearted lost her two beloved sisters long ago, a benevolent force deadened her sorrow-accidentally extinguishing all of her emotions. Yet whenever she encounters the vampire with his grave eyes, her feelings-particularly lust-emerge multiplied. For the first time, she's unable to complete a kill.

The prize is a key powerful enough to resurrect her sisters. Not understanding the key's import, Sebastian hinders her against other opponents by using her new feelings to seduce her and earn her love. But when Kaderin is forced to choose between finally killing Sebastian and reuniting her family, how can she live without either. . . ?