Hostile Planet. Wheel of Fire, #1

Sergeant Jerry Harper left the military nine years ago. The four Breeds of humanity are at peace, and he's just a landscaper now. He spends his days mowing lawns and his nights playing gigs with his band. Civilian life in the Wheel of Fire galaxy is quiet and steady, and that's the way he likes it. That steady life is interrupted when a colonel from military intelligence shows up. Jerry's old war buddy, Brandon Woods, has gone missing, and the colonel is assembling a motley group of rescuers.
He wants Jerry to join the team. Jerry owes Brandon his life, so he agrees to help. He travels to another planet and soon finds himself mired in interstellar politics. There's something psychological going on, too, a legacy of his last battle nine years ago. Finding Brandon is challenging enough by itself, but now those secrets from the past threaten to drive Jerry insane. He hopes he can grab his friend and get out without attracting too much attention, and he certainly doesn't want to risk starting another Breed war.
But he's on a hostile planet now, and it won't give Brandon up without a fight.