This review was first posted on Ruby's Reads. 
 I'll be honest: after Hawke and Sienna's book (Kiss of Snow), my interest in the Psy-Changeling series kind of waned. Don't get me wrong-I wasn't about to miss any book Nalini Singh chose to bestow upon the reading world-but KoS was the culmination of nine volumes of highly charged foreplay. There was no way that Tangle of Need could live up to that kind of promise. In a way, though, I appreciate the space that Tangle of Need gave me. It was the right kind of book to come after Kiss of Snow. There's no way I'd have been able to appreciate Heart of Obsidian as much as I did if it had been book eleven instead of twelve. Which would have been a travesty because Heart of Obsidian is a fantastic read. 
 Hawke and Sienna's book was nine volumes in the making, but I've been anticipating Kaleb's story almost as long. The waiting was different, though, because I knew that Hawke and Sienna were meant to be each other's HEA. In Kaleb's case, it was more a matter of worrying that his heroine would be worthy of the character. Another difference was that, throughout the series, we've been privy to a moment or two of Hawke and Sienna's perspectives, but never Kaleb's. He was an enigma-and if you know anything about me, you know I love a man of mystery. I don't usually worry too much about cover and blurb reveals, but the strip tease method of slowly revealing information about Heart of Obsidian had me checking Nalini's blog almost every day. I agonized over how much information (if any) I wanted to know about the book before I read it. 
 In the end, all I really knew about HoO before I read it was that Kaleb was the hero and that the identity of the Ghost was revealed in the book. I knew I was getting a review copy from the publisher because I had participated in the tour, but when it didn't come by the publication date, I was kind of relieved. I was more nervous about reading it than I had ever realized! Still, when it came, I didn't hesitate to dive into what turned out to be a book to rival my love of Kiss of Snow. I'd thought KoS would never have any real competition-but how wrong I was! (Note: Hawke 4-Eva!) 
 Heart of Obsidian sizzles with romantic and sexual tension-this is a Nalini Singh novel, after all-but it's also a game-changer for the Psy-Changeling series. Nalini packs so much into this one book that you'll turn page after page until the end suddenly smacks you in the face. And, incidentally, makes you wail with despair because you have to wait so long for the next book. I, personally, want to kick the Guild Hunter books in the shins because I suspect they're holding up the Psy-Changeling series. Except then I'd have to wait longer for Venom's book. Unacceptable. 
 When I reflect on how much I love the Psy-Changeling books, I tend to focus on the romance. Heart of Obsidian does the romance stunningly well, but also highlights Nalini's skill in world-building. I love (lovelovelove) series books with over-arcing storylines and Nalini Singh is the Queen, Empress, Goddess of that particular skill. HoO also puts paid to my preference for Changeling heroes. I've always liked them best, but after Hawke (*dreamy smile*), Kaleb is definitely my favorite. Complex, ferociously protective and on intimate terms with his dark side, Kaleb is a prime candidate for a Book Boyfriend. He's also lucky enough to have powerful, passionate heroine that perfectly suits him. 
 In conclusion: I loved this book. I'd recommend the entire Psy-Changeling series based on the fact that it builds up to this one. Just think of it-if you start this series now, that's twelve delightful books you'll be able to read in a row. If you've already read every book in the series except Heart of Obsidian, don't worry. It's as good as your wildest dreams hoped it would be.