In the ship beginning/gear up time
The mission begins aboard the ship, the Unending Dromedary. The acolytes (or Agents however you refer to them) are given the mission info by a Servo Skull with a sarcastic and sassy machine spirit that can communicate with them. The mission is as follows; the Inquisitorial agents are being sent to the world of Leuce to investigate the sudden loss of communication with the Mechanicus outpost and the other imperial outposts on the world (a Sisters of Battle Monastery and small settlement). The team is given 2-3 days on board in the warp (you may choose to use the special rules for this ship outlined in the ship section of this page). Upon reaching orbit the team notices something strange from orbit, sensors from the ship (depending on how cooperative the crew are) will show that it is a ship grave yard that was not there originally.
If the crew is uncooperative the team will deploy to the surface and choose between checking the outposts, or checking the strange objects on the surface that will be discovered to be space ships that were ejected from the warp and crashed into the planet. If they go to the Mechanicus base they will discover that the base has a rope bridge across a river of green liquid (DM can decide to make it a harmless but annoying river of paint or toxic chemicals, also they will discover that if they walked/or rode a chimera another kilometer they would have found a sturdy metal bridge) since the bridge is swaying as they cross they have to take an agility test to keep balance if failed roll a d6 or flip a coin on a 4+ they have fallen in. Inside they will be directed towards the Arch-magos in charge of the operation and told about how the ships that crashed into the planet destroyed their communication array and killed their astropaths who were taking a walk in the fields of multi-cellular Eukaryotic Organisms that photosynthesize their nutrients. They would have the communications array up and running in a few days. The team reports this and is ordered to investigate the ships on the planet. As they approach the ships they notice not all are of imperial make. The closest one they come across is designated high priority by the Servo skull. It is an inquisitorial freighter belonging to the Inquisitor they are serving. Inside they will find some object possibly a book on prophesy or about a demon that is about to be resurrected on a nearby planet. Inside the ship are mutated crew members who are brain dead and ruthless killers. Also the object is in a square room with gun servitors that fire automatically unless identified the acolytes identify as inquisitorial agents or steal an ID badge from a mutant crew member.
Exiting the ship
As they leave the ship with whatever they find, they are ambushed by some xenos life forms, suggested are orks, tyranids, Dark Eldar, or tau. These xenos are part of an invasion force determined to conquer the planet for some reason. The team will fight it's way out to either the landing zone or one of the Imperial outposts on the world. From there they are sent to defend the communications array until it's completed and the inquisition/ allied forces can be called in. They will be aided by at least 2 squads of Inquisitorial Storm troopers. They will have the chimera they rode in if the DM allowed them one. They may also request forces from the Soritas and whomever they can muster if the GM wills it.
from here the DM is given total free reign to do whatever the heck he wants. He should make the defense a challenge with waves after waves of enemies at least. Then he can follow where ever the book/artifact leads them and possible to search for the origins of the invasion (not applicable for tyranids)
-Scenario written by BenBigmac