Though labeled a sequel to Old Man's War, The Ghost Brigades is very much a stand-alone adventure. While it expands upon ideas introduced in the earlier novel, John Scalzi doesn't require you to have read it to become fully absorbed in this one. I have a soft spot for writers who are this thoughtful. There's nothing that chaps my skinny butt more than the realization that in order to read an author's new work, I have to come up to speed by reading his previous eight or nine. Series fiction may rule SF and fantasy publishing these days, but there's much to be said for allowing your readers an onramp at any point they choose.
It's fitting, then, that choice is one of the themes at the center of The Ghost Brigades. That, and identity, which Old Man's War addressed but Brigades tackles full-on. Both novels are set in a future in which human colonial worlds are defended from the ravages of innumerable hostile aliens by the Colonial Defense Forces, most of whom are made up of conscripts signed up as senior citizens and then given fresh new enhanced bodies to fight with. The theory is that melding the experience and wisdom of age with the vitality of youth will make for a more formidable soldier. But the CDF has another breed of soldier, the Special Forces, nicknamed the Ghost Brigades, whose bodies are created from the DNA of recruits who died of natural causes before their training could complete, but whose minds are entirely blank, their neural pathways forced into accelerated development by an implanted technology called the BrainPal. They are adults without childhoods, humans with neither a past nor any identity that their BrainPal hasn't established to serve the CDF's military goals. They aren't mindless automatons, but they aren't quite people either.
When the CDF gets wind that one of its best research scientists has turned traitor and sparked an unprecedented alliance between three other species to wipe out humanity once and for all, drastic measures are called for. As it happens, said scientist, Charles Boutin, tried clumsily to fake his own death, but succeeded less clumsily in storing a copy of his consciousness in a computer, something never before achieved. The plan is to create a new Special Forces soldier with Boutin's DNA, but rather than leave him a tabula rasa, try to implant the copy of Boutin's consciousness into the new brain, to learn where Boutin has escaped to and what his intentions really are.
But the attempt at the latter doesn't seem to work. So the new soldier becomes a regular grunt in the Ghost Brigades, given the name Jared Dirac and assigned to a platoon commanded by Jane Sagan (who figured prominently in War). On the off-chance that Boutin's consciousness does in some way begin to emerge, Sagan and her superiors are determined to keep an eye on Jared. Well, emerge it does, gradually (shades of A Scanner Darkly), and when the extent of Boutin's treachery becomes known, it's clear there will be some difficult choices required to stop him.
Conscience, choice and identity all gather on Scalzi's thematic playground here. Can a being like Jared, or any of the Special Forces soldiers, truly exhibit free will and execute responsible choices if they were designed for a particular purpose? Scalzi couches these themes in a narrative approach that's nothing short of a masterstroke: he pits one specially created race of beings, the Ghost Brigades, against another, the ruthless alien Obin, a species engineered into existence by yet another more advanced species simply to satisfy their scientific curiosity. The Ghost Brigades have no frame of reference for their own existence outside of their military service to the CDF; the Obin have intelligence but nothing you could call a conscience, that makes their goals in life anything other than purely functional towards fulfilling certain species imperatives. The Obin wage war relentlessly, but not out of hate. It's that they know no other means to get what they want. Can either group choose a path not predetermined for them by their designers? Neither group could reasonably be said to possess free will in the sense that you or I enjoy it, and we're immediately prompted to wonder what degree of free will we actually enjoy. Is what we call our free will always going to be limited by the nature of what kind of being we are? (As much as I might want to fly, flying will not be what I do if I jump off a cliff. Do I then lack free will?) Or is free will just an abstraction that our ability to cheat (I know, I'll invent an airplane!) becomes a measure of our advancement as a species?
Like Old Man's War, The Ghost Brigades is thinking fans' space opera. And for all that Scalzi gives you to chew on intellectually, he doesn't skimp on the blow-shit-up factor. The book opens with a fantastic action scene that ends with a brilliant narrative bait-and-switch I didn't see coming, and climaxes with an even better one that brings Jared to a logical and satisfying fulfillment of his destiny. If Scalzi stumbles at any point, it's that he flirts dangerously with mawkishness when he introduces the character of Boutin's little daughter Zoë, whom Jared even has an attachment to once Boutin's memories begin to resurface in his mind. Zoë serves as a motivational lynchpin for the actions of both hero and villain, and while in the end I thought he kept her safely away from Spielbergian cuteness-overload, it's dead obvious by the clear affection with which Scalzi has built the character that she's inspired by his own daughter (whom he has turned into a full-fledged web celebrity on his popular blog). And maybe this affection overtook any concern he might have had that the whole child-as-catalyst-for-character-arc thing is just a little clichéd.
But this is such a minor factor that it doesn't in any meaningful way affect the novel's success or sabotage its goals. The Ghost Brigades maintains Scalzi's standing as one of SF's most rewarding purveyors of thrilling, gut-wrenching, and thoughtful space opera.