To hell and back . . . Though he has vampire, demon, and Viking blood rushing through his veins, Ivar Kjeidsen’s soul-crushing trip to hell broke him in ways he can barely fathom. One vow keeps the deadly immortal standing: To rescue the vampire brother who had sacrificed freedom for him. To do that, Ivar needs the help of a brilliant physicist with wary brown eyes, fierce brilliance, and skin that's way too soft. Dr. Promise Williams understands the underpinnings of the universe but has never figured out the human beings inhabiting it. Her function is to think—and not feel—until she’s touched by a vampire who’s nowhere near human. The primal hunger in his eyes awakens feelings in her that defy calculation. As she shows him the way to step between worlds, he brands her with a pleasure that could last more than a lifetime . . .