You wouldn't think a novel set in a post-apocalyptic future where nearly everyone is living on the edge could be described as "fun", but that is the best way to describe FIREFIGHT. The second novel in a trilogy about "Epics" - superhumans who gained powers which immediately corrupted them - the story picks up shortly after STEELHEART (well, technically after MITOSIS which was an interim novella but is not necessary to enjoy the book).
