I reveal the main characters identities, so if you want to remain unspoiled on that stop here.Like with most books in the Psy/Changeling series, I had multiple ratings in mind for Heart of Obsidian, each for different aspects of the story. Overall I'd give it a bit less than 4 stars. The romance between Kaleb and Sahara was the best part of this book. It was mostly just the two of them for the first half, with very little interaction with others. I got to know them; their intimacy felt organic, especially compared to Hawke/Sienna (yeah, I'm still bitter about that pairing)and Riaz/Adria--I never really got those couples. I did have some issues, though, mostly with Kaleb. Kaleb is a former Councilor, and like all Councilors, has committed all kinds of immoral acts to get ahead. Authors typically go one of two ways here--either a full on redemption, atone for past sins story, or a "but s/he had perfectly legitimate reasons for doing those evil things so it's okay" story. Unfortunately, Singh chose the latter, and it felt like a cop-out. To be fair, I go back and forth with that type of character and with redemption stories in general; chances are good I wouldn't have been completely satisfied with the first option, either. While I need true redemption when it comes individual relationships, when it comes to characters who do bad things on a larger scale I'm more ambivalent. I don't want every bad guy to turn completely good (and it's not like Kaleb's ends up a boyscout), even when the bad guy becomes the hero. Though I have no idea if such a hero could actually work, so...my feelings on this are complicated, is what I'm saying.(A tangent to illustrate the point--I adore the character of Nikita. At the start of the series she was a perfectly Silent Councilor and unfeeling mother to Sasha, and the way things have evolved we now know that she's done a lot to protect her daughter over the years. She's also gone against Psy rules to help others when it aligns with her interests. That's enough good for me. I worry that she's going to be completely whitewashed by the end of the series, when what I love about her is that she's smart and ruthless and does things--good and evil--for personal gain without being a complete monster. I don't want all characters to be so morally ambiguous, but Nikita still is and that's what Kaleb should have been at the end of this story.)The overall plot was a mixed bag. Kaleb and Sahara are both Psy, which is great for two reason: 1)No mating drama--and after they way things went down in the last two books, I really needed a break from that. I've never been a fan of the concept, but KoS and ToN officially made it dead-to-me. 2)We got a much closer look at the going-ons of the PsyNet and the ongoing civil war. I've always found the Psy to be the most interesting of the three races, so that was a big plus.The problem with the Psy/Psy pairing is how little we see of the other races. While I didn't miss anyone per se, seeing the Psy, Changelings, and Humans strategize and deal with each other--the complexity of those relationships--is a highlight of the the series for me. Their absence for most of the book may have led to a stronger romance, but Singh's world-building throughout the series is excellent, and I read it primarily for that reason. (This wouldn't have bothered me if HoO were book #4 instead of #12--it's more about my expectations than anything wrong with the storytelling.) This book isn't the end of the series or the current story arc, though I'm at a loss as to where the story can go from here. I do think there's more story for Kaleb, since he ends up taking over the Net as a sort of benevolent dictator, which, if we're talking true freedom for the Psy, isn't exactly ideal. Democracy, anyone? It'd be interesting to explore that, but I didn't see any hint of it. Of course, there are still plenty of characters to write about and pretty major hinting about who the next book will focus on, but the major conflicts that the series has been dealing with feel mostly complete.