This book bears a lot of similarities to Lisa Henry's Tribute, which I read first but was published later, so I cannot help but think of the books in relationship to each other. Both stories deal with the experience of a young prince being given as a sex slave to a warlord as part of a peace treaty. The comparison does not harm either book, because unsurprisingly the authors focus on very different things.
[Mild Spoilers Alert]
Concubine is not as stressful a read for several reasons. The bond between the main couple forms earlier and is from the outset more affectionate. Kael in Concubine does not suffer the kind of anguish and uncertainty that his counterpart, Kynon, does, and he is given much more freedom to show his personality, to speak his mind, and spar verbally with his master; Ms. Knowles is not interested in showing how a person is broken and reformed by slavery, so much as how he discovers a true if hidden desire. I found the love scenes sensual and very steamy; though Taren definitely demands a very thorough submission from Kael, the overall focus was not so much on humiliation or cruelty but very much on pleasure. It really did not read like a dub-con or non-con scenario to me, but more like a breaking down of artificial societal barriers, though I realize it may read differently to others.
The main external conflict with the concubines guild was not the most interesting part of the story. I would have liked a more developed reason for such a deadly antagonism. But overall, I really enjoyed reading the book and will probably read it again.