I want to write a mission which is based off the RoB joint operations section where a single battle brother goes into the calixis sector

looking for a senior servent of the imperium whos infected:

I really like the idea of him getting involved in the conspirices there and I was thinking that an ordo xenos inquisitor

that served as an acolyte to the same master as camillus can do his best to help him and will be his source of requsition.

although I need some help

1stly what job could the target play in the imperium as I cant think of somthing suitable

also what can he be infected by? Im a bit stumped on this one

lastly how can I make him get involved in the conspirices? because I dont know much about the calixis sector

oh yeah and i'd also like the target to be aware that hes coming and send kill squads after him and a very deadly bounty hunter

who use to be an astartes.....

As to the infection Chaos is the obvious and frankly predictable answer. A more interesting idea could be either some form of Xenos like the genestealers or some other home-made foul horror from the stars or perhaps even a Halo Device. Or you could have it that some loathsome heretek has infected the target with some manner of perversion made to create a perfected human, and which turns the target into a monstrosity as the virus overtakes and reshapes the biological structure.

The Infected could very possibly be a Chartsit captain that transports equipment between Calixis and Jericho.

The infection could be any number of things, but if you want to keep it Xenos related Genestealers are a very nice option since they can fill pretty much any kind of role you want (Cult investigation, Murder mysteries, all out combat etc). Deamonic influence is another possibility if you like that twist, it isn't very DW'y though (they hunt mostly Xenos after all). You could however go for a different approach and have him not being physicly infected but instead mentally by the Taus ideals. The marine then have to stop him before those ideals can take hold in Calixis.

You can also cook-up something of your own devices.

As for knowing the marine is coming, maybe the marine have tried to kill him allready but failed? I would imagine it quite hard for a Space marine to keep in hiding from someone actively searching for you.

Infected with?

How about being infected with an idea? The source of all corruption, wickedness, and Heresy of course. Maybe they doubt the God Emporer's divinity/think He's dead/think He's the fith Chaos God? Or they believe that the Ministorum have no motivation beyond self service, or that that the lives of everyday citizens would be improved by the dissolution of the Mechanicus, or even... ... even just doubting whether the Inquisition actually serves a useful purpose. Perhaps as Bassemandrh suggested they have become agents for the Tau, infected with the idea of the greater good, and they are obsessed with spreading that idea?

I would suggest checking out the various radical Inquisitorial factions as a place to get ideas.

Oh yes, Burn the Heretic, Purge the Unclean, ZAP! ZAP! ZAP!

Target's job- Adept in the administratum(huge orginization, plenty of access.)

Infected with- Slaugth bio-tech

The kill squads may have data pads with information on them that the kill-marine can back track.