I wavered between four & five stars because the question I usually ask myself is, "Would I read this again?" Yes, I would. Singh has been building her world carefully, paranormal brick-by-brick, and Heart of Obsidian is the climactic novel that was needed to pull it all together. A hero and heroine made for each other, and a love story that builds in a spectacular fashion. Fans of the series will consider this a must-read. For others, it's liable to be too much going on to absorb from one book, but for those readers waiting for this story, it's an instant classic.