I never fail to enjoy a Nalini Singh book and Heart of Obsidian was no exception. Many questions were answered in this book which I was glad of as sometimes if a revelation or under-lying story is too delayed I begin to lose interest. The suspense was built perfectly by the previous books without over doing it, now I feel my patience has been rewarded and I look forward to seeing what happens in the fallout from this book. 
 This series has so many fantastic characters each unique and individual meaning that I always hotly anticipate the release of a new Psy-Changeling book knowing how unlikely it is that I'll be disappointed. This book having been perfectly set up in Tangle of Need does not fail to deliver. Many things come together in Heart of Obsidian (view spoiler)[from the disappearance of Faith's cousin mentioned in Visions of Heat to the child that lifted the bullet train off Annie in Stroke of Enticement (hide spoiler)]. 
 (view spoiler)[ It made sense to me that Kaleb's heroine would be someone who had known him in childhood before his Silence was total. The character we've seen in the series so far is too driven, ruthless and Silent to allow himself to be vulnerable enough to care for someone that deeply otherwise. Along with what we already suspected was a traumatic childhood at the hands on Santano Enrique - a fact which as Sahara points out everyone seems to forget focusing only what the results might be now rather than brutality that Kaleb endured from three years old - Kaleb couldn't fail to be anything other than a dark character. He remains true to this, making the story that much more believable. He wants a bond to form between himself and Sahara and is willing to use physical intimacy to achieve it, not realising how much it will affect him when coupled with the unwavering loyalty he feels to the only person he feels has ever truly cared. Sahara also proves her strength as a survivor. Despite her subconscious telling her Kaleb can be trusted she has no way of knowing if this is true without her memories and so acts accordingly with wariness showing her keen intelligence which was vital for her to survive seven years of captivity and torture. For me the most magical part of their relationship was Kaleb's unflinching devotion and loyalty to Sahara, something I never doubted throughout the book. (hide spoiler)] 
 This is a book that moves the over-all story arc forward considerably without compromising on the development of the relationship between Kaleb and his heroine. For me this book should read as part of the series rather than stand-alone in order to understand the events taking place which are a key part of the story. An exciting addition to an already fantastic series I can't wait to see what happens next in this world as a result of the events in Heart of Obsidian.