I have an old backdrop for a WH40K thread I ran on a different role play website. It's a quick read:
The Astronomican has once again intercepted a message of the utmost priority. Abaddon the Despoiler, warmaster of the Chaos Space Marines Black Legion has uncovered the general whereabouts of an ancient chaos relic.
Dated back from the dark period of the Horus Heresy, this relic had been abandoned on a planet that bore no fruit of life. Located to the Galactic East, in a cluster of planets named the Chronus Rift, this icon of chaos had originally belonged to the primarch of the World Eaters Space Marine Legion, Primarch Angron, and is said to possess a vast amount of power that Abaddon covets. He dispatches of splinter fleet to go forth, towards the Eye of Terror, where this system of planets is located, to find this relic. What the Astronomican recieves is simply the location of the drop zone for these splinter troops, not the location of the relic itself. Planet GS00983
The Imperium must act quickly, it passes on the information to the Ordo Malleus, who in turn proceeds to dispatch a number of Inquisitors along with the Sisters of Battle. Taking absolutely no chances, a sect of the Space Marines, along with various elements of the Imperial Guard are also sent; there is no mistaking that this relic of chaos must be destroyed before it falls into Abaddon's hands.
As with any time a sect is dispatched, there will be splinters of those who will arrive earlier than others. Their mission will be to conduct reconnaissance and set up a secured area of operations in order to prepare for the main arrival of those dispatched from the Ordo Malleus.