The Ordo Hereticus is the branch of the Inquisition that hunts the enemy within: the heretic, the mutant, the rogue psyker, and the traitor who wears the mask of loyalty. Where other Ordos face daemon and alien, this one confronts the far more insidious rot that spreads through Mankind's own soul, for a single charismatic apostate can turn a compliant world to open rebellion in the space of a generation. Its Inquisitors are watchers of watchmen, holding even the Imperium's most trusted servants to relentless scrutiny.
The Ordo rose to prominence after the Age of Apostasy, the terrible schism in which a mad High Lord of the Ecclesiarchy nearly drowned the Imperium in fratricidal war. In its aftermath, the Inquisition resolved that the state church itself must be watched, and so the Ordo Hereticus took as one of its foremost charges the surveillance of the Ecclesiarchy, ensuring that faith never again curdles into tyranny.
To carry out its purges the Ordo commands a formidable Chamber Militant, the zealous battle-sisters of the Adepta Sororitas, whose incorruptible devotion makes them the ideal instrument for cleansing corruption from holy places. Alongside them march witch-hunters, arco-flagellants, and penitent hosts, all bent upon the extermination of the impure.
The Ordo Hereticus treads a delicate path, for the very institutions it polices are those the Imperium relies upon to function. An accusation carelessly made can topple a cardinal or spark a war, and so its Inquisitors cultivate patience alongside their zeal. Their remit and their methods are detailed in the glossary account of the Ordo Hereticus, guardians against the day when the Imperium's own faith becomes its undoing.