The Ordo Hereticus – by far the biggest of the Ordos – hunts the enemy within. The Ordo Xenos watches the enemy without. Then there are the lesser Ordos – they watch other stuff – but they are hardly worthy of mention in this context. Lastly there is the Ordo Malleus...they deal with...whatever comes after. When the Hereticus fails to contain the witches and sourcerous flames rise from the dark abyss; that is when you make for the nearest exit, leaving the men in the hooded grey cloaks to sort out the mess.

That is the way the Ordo Malleus will be portrayed in this campaign. They are Special Branch if your will. In the basic setting for Dark Heresy the Ordos are more equal I suppose, but seeing as how the overt threat of Chaos will be somewhat downplayed, this version fits better with the overall campaign theme.

Actually, come to think of it, you're not entirely sure exactly what the Malleus does, but you're petty sure you don't want to know...