Book 54 in the New York Times Bestselling series The Horus Heresy. Discover the last battles leading to the Siege of Terra... The skies darken over Terra as the final battle for the Throne looms ever closer... As the Traitor primarchs muster to the Warmaster's banner, it is Mortarion who is sent ahead as the vanguard of the Traitor forces. But as he and his warriors make way, they become lost in the warp and stricken by...