Darkness is rising on Achyllus Prime. Severin Drask, sorcerer lord of the Crimson Slaughter Chaos Space Marines, works to harness the power of the Temple of Shades and unleash a tide of daemons upon the Imperium. All that stands against him is an Execution Force of the Officio Assassinorum, four Imperial Assassins - Vindicare, Callidus, Eversor and Culexus -who must set aside their distrust and fight as one if they are to kill Drask and thwart his evil plan.