"War within the shadows"
- —Book's tag-line
Nemesis is the thirteenth volume in the Horus Heresy series of novels.
After the horrors of Istvaan V, Horus declares outright war against the Imperium. In the shadows of the Imperial Palace, powerful figures convene. Their plan is to send a team of assassins to execute the Archtraitor Horus and end the war for the galaxy of mankind before it has even begun. But what they cannot know is that another assassin is abroad already, with his sights firmly set on killing the Emperor.
Nemesis is set approximately two standard years after the events on Istvaan V described in Book 5, Fulgrim. It deals with a plan by a secret Imperial organization, the Officio Assassinorum, to eliminate Horus using an Execution Force drawn from all the "clades" (predecessors of the Assassin Temples) that make up the Officio Assassinorum. There have been several previous unsuccessful attempts against Horus' life, and this gives a high-ranking officer of the Word Bearers Traitor Legion the idea to field a Nemesis Weapon of his own (a highly specialised assassin) in an audacious scheme to kill the Emperor of Mankind.
- Nemesis (Novel) by James Swallow