Vanity is an imperial hive world under great pressure. It is currently only about 40% occupied by imperial forces. The rest is under heretical control by a combination of civilian radicals and tainted marines. The blood talons have been in constant battle on Vanity, and with occasional aid from the ordo hereticas.
There have been confirmed sightings of influence from multiple chaos gods, but they are having a great deal of trouble confirming just what enemy they are facing.