I'm impressed by this writer.
This isn't really a mystery, I guessed the `answer' in about 10 pages (and I can watch/read about any detective story and not get who dunnit until we get told in the last 10 minutes/pages). But it is compelling. Just at the point I was going to give up on it as just a BDSM version of victim fiction, we're given the story of how Andrew and Thomas met. This re- engaged me, and made me sympathetic to both Andrew and Thomas; I had to find out how/if they resolved their issues.
This book doesn't have huge amounts of BDSM sex in it - if you want that go for Sean Micheal's `Bent' et al books or Chris Owen/Jodie Paynes' `Dominations' series - what it does do is powerfully illustrate one of the variety of power exchanges that can exist in BDSM relationships.