I wasn't too sure about this when I started reading. I was afraid the blood fetish aspect would be a bit hard to grasp and would feel unrealistic. While that is the main issue that sets this story in motion, it goes so far beyond that, you almost forget it was the real problem to begin with. It didn't take long to see that Logan was a more serious and experienced Dom than he first appears.
For me, this is a story of misunderstandings and things getting out of control. Logan loses control with his blood fetish, which he tries to curtail with a more fulfilling relationship than he had in the past. The doctor/patient lines are crossed, though Kasper does seem to helping Logan. When he Kasper is submitting to him, it is almost as though Logan forgets about the blood fetish for a while. But then things get out of hand for Kasper, as he continues to push and manipulate Logan into giving him more pain. Logan realizes he cannot give Kasper what he needs without breaking his own boundaries and steps back, which sends Kasper on a course of destruction and addiction.
Logan steps back in to try and help Kasper get healthy again. Kasper finally comes to the understanding that he seeks the pain because he believes that is the only way he can reach subspace. The story then changes to their journey into finding safer ways to achieve this and find the peace and fulfillment they are each seeking.
The BDSM is a very big part of this story, and while some stories seem to go over the top with scenes almost for shock value, this one does not. One thing that I found very refreshing was Logan's insistence that Kasper NOT call him Sir. I'm looking forward to reading more about these guys.