Nemesis

Horus has declared open war on the Imperium in the wake of the atrocities at Isstvan V. The conflict is still young, and in the shadows of the Emperor's Palace a group of powerful figures meets to decide how to stop it.

Their plan is a covert one. They will send a team of assassins to kill the arch-traitor Horus, ending the war for the galaxy of mankind before it has properly begun.

They do not know that an assassin is already at work. Horus has despatched a monstrous killer of his own, and this one has the Emperor as his target.

This is a Horus Heresy novel. The Heresy is mostly a war of Space Marines against Space Marines, but this book turns to the other combatants who work out of sight. It shows the precursors of the Assassinorum temples familiar from Warhammer 40,000 in action. Expect a story of covert operations and rival killers rather than open battle lines, with a strike at each side's leader as the stake.