Ordo Necros
The Ordos Necros is only five Inquisitors strong and shrouded in mystery. What's more it has an Ordos of unknown size specifically to watch over it. There are a number of theories as to the intent and area of study, here are just a few.
The most straight forward theory is the Ordos Necros studies death, simple as that.
The most fluffy theory is that the Ordos Necros are death cult assassins of so much skill and loyalty they were incited into the ranks of the Inquisition and have hence forth dedicated them selves to bringing the art of the sword to as many planets as possible and possibly designing and researching now methods of blade based combat. It also makes sense that other Inquisitors would want to keep an eye on them.
Based on the hazy link between 'Necros' and 'Necron' some believe the Ordos Necros study the Necrons, which would explain why they're so secret as so far no technology has ever been stolen from the Necrons.
Finally the least likely but perhaps most interesting theory is that the Ordos Necros studies the Legion of the Damned, each as secretive as the other, it would make sense for the Inquisitors to want to keep track of the comings and goings of these mysterious zombie/ ghost/ space marines.
