Hereticus

Book 3 in the Eisenhorn series

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? This edition also includes the short story ‘Backcloth for a Crown Additional’. Eisenhorn seeks the truth behind a string of disappearances centred around a travelling carnival and a pictographer whose images are more than they seem.

Read it because

Inquisitor Eisenhorn has saved worlds and beaten bad guys galore – in short, he's a hero. But he's also done some dodgy things, and they're coming back to haunt him... His struggle to justify his actions (especially the daemon summoning) make this an incredibly compelling read and rounds off the trilogy perfectly.