His Last Command (Warhammer 40,000: Gaunt's Ghosts: The Lost, Book 2)

Returning from a long mission on a Chaos world, Commissar Gaunt finds that his old regiment - nicknamed Gaunt's Ghosts - has been disbanded and redeployed under a new commander. But when the fighting becomes bitter, Gaunt is finally reunited with his men as the Imperial forces make one last attempt to hold the line against the invaders.