The heresy of Horus reaches the Solar System — will the defenses of Rogal Dorn and his Imperial Fists withstand the onslaught of enemies? Recalled from the fields of the Great Crusade after Ullanor, Rogal Dorn and his Legion were appointed by the Emperor's Praetorians, but only after the Warrior's treachery was revealed, The full extent of the sacred duty incumbent upon them becomes evident.. Now, the Solar System is under attack for the first time since the start of the war, and many seemingly impregnable fortifications prepared by the Legion of Imperial Fists prove insufficient. All eyes are on this new threat coming from outside the Gate of Terra, but who will protect the Primarha Dorn from internal enemies?