Warhammer 40k - Imperial Fists Novel - Seventh Retribution by Ben Counter

The world of Opis is wracked with civil war and in danger of being lost to mankind’s Imperium. But more than just rebellion lurks on this once-peaceful world. Captain Darnath Lysander, hero of the Imperial Fists and captain of their elite First Company, leads his battle-brothers in prosecution of the traitors. Tortured by memories of his time imprisoned by the Iron Warriors, Lysander finds himself thrust back into that horror as the Ruinous Powers are revealed to be behind the treachery. Beset by monstrous foes and allies he cannot trust, Lysander must rally his Space Marines to defeat the master of the enemy hordes before all of Opis is consumed by the insidious powers of Chaos.