Hunted by his former allies as a radical and enemy of the Imperium, Inquisitor Gregor Eisenhorn must fight to prove that he remains loyal as he tracks down a dangerous heretic whom the Inquisition believes dead - the dread former Inquisitor Quixos. As he grows more desperate for victory, Eisenhorn uses ever darker means to achieve his goals - but how far can he go using the weapons of the enemy until he becomes that very enemy - and no different to the traitor he hunts?