Following up is hard to do. But 'The Ghost Brigades', John Scalzi's sequel to 'Old Man's War' makes it look as easy as fighting of a brace of alien species on a variety of planets with a fighting force comprised entirely of aging retirees and dead people. It's a dirty job, and if anyone has got to do it, it might was well be those wrinkly and post-wrinkly types we'd prefer not to see unless they’re advertising insurance or laxatives. 'The Ghost Bridges' is a substantially different novel from 'Old Man's War'. John Perry, the hero of the first novel is offstage for the proceedings, and we have mainly Jane Sagan on board offer a bit of continuity. Humanity is still under fire, but this time around our hero isn’t just old, he's dead. The narrative here, however is not dead. This is a lively, exciting space adventure that is more cohesive than 'Old Man's War' with an emotional reward as thrilling the many battles.

'The Ghost Brigades' begins with a very nice twist, and continues to dance elegantly until the final page is turned. A captured alien Rraey decides to live and offers up a bit of crucial intelligence to the Colonial Defense Forces. Charles Boutin, a military scientist thought to have committed suicide has defected. Three alien races are joining forces, making use of what he told them, and ganging up to attack humanity. The CDF's only hope is the Special Forces, aka theGhost Brigades. These are the old people who manage to kick the bucket before they can get upgraded into kick-ass CDF soldiers. Neither wasting nor wanting, the CDF uses their DNA to grow modified military-issue clones of the originals. Wave your hand and you've got a one-year old human who is fully grown and ready to fight. Flip a switch and you've performed an experimental consciousness transfer from the traitor scientist into a CDF grunt. If the brain swap doesn't take at first, end him out into battle and hope the ensuing trauma triggers a change of mind if not heart.

Scalzi is firing on all cylinders here. 'The Ghost Brigades' offers up one great battle scene after another, with finely developed characters and a wonderfully developed look at youth as opposed to the vision of the aged we enjoyed so much in 'Old Man's War'. Jared Dirac, the soldier created in an effort to scare up Boutin is bonded to his squad and sent into hell several times over. Scalzi rattles off a huge cast of characters in a compact novel and makes the reader care greatly about every damn one of 'em. His aliens are inimical and powerful enough to kill off people we like and as cagey as conmen. There's not a false note in any of the characterizations, whether they walk on to get clobbered or keep coming back, sometimes from the dead for more. These are vibrant, rocking men and women that willstay with you long after you finish the book.

As for the action, it's constant but the plot is tighter with lots of great twists. 'The Ghost Brigades' has some of the episodic feel of 'Old Man's War', but the through-line is stronger and more integral to both the characters and the action. This alien three-way leads to some superb set-pieces that advance both plot arc and character arc.

Scalzi uses his premise to explore youth in a wonderfully developed discourse on babies. This is not at all what you might expect a rock'em, sock'em science fiction novel to do, and it makes for a delightful reading experience. There's lots of conceptual meat to chew on while men and women jump out of orbiting spaceships to descend for battle on an alien landscape.

'The Ghost Brigades' pretty much has it all, and has it better than even the excellent 'Old Man's War'. Oh, the aliens are still rather vaguely described, but one can attribute that to Scalzi's very admirable decision to strip down his novel to the bare necessities. There is not an ounce of fat or excess here. This is not to say that Scalzi scrimps on the emotional component; indeed, it’s the touchy-feely part that makes this book so good. There's no unctuous sentimentality. Shoot an alien, shed a tear. 'The Ghost Brigades' is as lean and mean as the universe it describes.