The Ordo Hereticus is the branch of the Inquisition charged with policing the Imperium from within, rooting out the heretic, the mutant, the rogue psyker, and the traitor. It watches humanity itself, and even the great institutions of the Imperium, for the first signs of corruption and rebellion.
Sometimes called the Witch Hunters, the Inquisitors of this Ordo emerged when it became clear that faithlessness and false faith could rot the realm as surely as any alien invasion. They scrutinise the vast Ecclesiarchy for signs of dangerous cults, hunt psykers who escape sanctioning, and stand ready to condemn any world that strays into apostasy, no matter how highly placed the guilty may be.
In their crusades against heresy, the Ordo Hereticus works closely with the Adepta Sororitas, the militant sisterhood whose zealous faith makes them ideal instruments of purgation. Together they bring fire and judgement to the impure, for in a realm held together by belief, the wavering of faith is treated as among the deadliest of all threats. Mercy is a luxury the Ordo Hereticus seldom permits itself.