The Ghost Brigades is John Scalzi's follow up to Old Man's War and he goes in depth with the mysterious Ghost Brigades from the first novel. The Ghost Brigades are elite Colonial soldiers engineered and changed from the DNA of dead humans. Those who die after signing up to be part of the Colonial Defense Forces have already given their DNA to the CDF and their death allows the CDF to use that DNA as a template to redesign the Ghost Brigades into something more than human and much more deadly.
In Old Man's War we were introduced to Jane Sagan, an elite soldier engineered from the DNA of the wife of that novel's hero John Perry. Jane is one of the two primary characters of The Ghost Brigades and through Jane as well as Jared Dirac, a rookie (meaning newly born) elite soldier we learn the truth about what the Ghost Brigades are and about the soldiers. This is not the main point of the novel. The novel's storyline revolves around the Brigades on a mission to find a scientist, Charles Boutin, who betrayed the Colonials to an unfriendly alien race. Dirac holds the key to finding Boutin because Dirac was created with Boutin's consciousness, a consciousness which has not come forward yet so Dirac has no idea that he is also somebody else.
Old Man's War raised a perhaps unfair level of expectation for all future work of John Scalzi. There was a sense of discovery and wonder about that first book that would be difficult to match. The newness has worn off a little bit in The Ghost Brigades but Scalzi's high level of quality and craft in writing a fast paced, interesting, original, intelligent, action packed, compelling science fiction novel is enough to keep me coming back for more. The Ghost Brigades is not Old Man's War and nor should it be. The Ghost Brigades is a damn fine book with a story I was not yet prepared to have end. Scalzi is the science fiction author to watch.