The Ghost Brigades (Old Man's War, #2)
From the back cover: The Ghost Brigades are the Special Forces of the Colonial Defense Forces, elite troops created from the DNA of the dead and turned into the perfect soldiers for the CDF's toughest operations. They're young, fast, strong, and totally without normal human qualms. The universe is a dangerous place for humanity -- and it's about to become more dangerous. Three races we've fought before have allied to halt our expansion into space. Their linchpin: the turncoat scientist Charles Boutin, who knows the CDF's biggest secrets. To prevail, the CDF must find out why Boutin did what he did. Jared Dirac -- a superhuman hybrid, created from Boutin's DNA -- is the only person who can provide answers. Jared's brain should be able to access Boutin's electronic memories, but when the memory transplant appears to fail, Jared is given to the Ghost Brigades. At first, Jared is a perfect soldier. Then, as Boutin's memories slowly surface, Jared begins to intuit the reasons for Boutin's betrayal... and the fact that some of humanity's enemies have worse things in mind than our mere defeat.