War Machine by Andy Remic

In a time of post-Singularity and FTL travel, Combat K are elite and murderous combat squads trained by the Quad-Gal Military specialising in interrogation, infiltration, assassination and detonation. Their gameplan is simple: to end The Helix War, which had raged across galaxies for a thousand years. Ex-soldier Keenan, a stocky battered war veteran, addicted to Jataxa spirit yet still horribly efficient at his job, is working as a private investigator on a planet at the peaceful fringes of the Quad-Gal. Following the death of his family, Keenan is riddled with guilt and self-loathing, and carries a need for revenge which consumes him. When a prince from Jervai Province offers him a case on a dangerous colony world in exchange for clues that may lead to his family's murderer, Keenan is dragged from his self-pity. However, to have any chance of success he must gather together his old military unit, a group who swore they'd never work together again... Through the tribal jungles of Ket, the mean chaotic streets of The City, the mission leads the squad to Teller's World, a Dead World, and home of the extinct God Leviathan... and there Keenan will find answers to his deepest nightmares... and face an ancient, evil terror older than The Four Galaxies.