For his seventy-fifth birthday, John Perry visits his wife’s grave and enlists in the Colonial Defense Forces. The CDF remake him and his peers into supersoldiers with decades of experience in enhanced bodies. Their mission is to protect the human colonies and to take new worlds. It’s an alien-eat-alien multiverse (sometimes literally) and the habitable planets are much contested.
Scalzi owes a debt to Robert A. Heinlein (acknowledged at the end of the book). The wise old man, the citizen soldier, enduring love, youth regained—some of RAH’s favorite topics. Too, it owes not a little to Joe Haldeman’s The Forever War: disillusionment, soldiers as pawns.