The emanciated head of something Karnak Zul calls the 'Dusk Hag'. Apparently she was a diviner of some skill until the Inquisition got to her. Her name derives from two sources: Firstly the death world of Dusk, located on the rimward edge of the Malfian sub-sector/Calixis sector, close to the edges of the Screaming Wortex (a warp storm of some size and repute; it separates Calixis from the Koronus Expanse and the Halo Stars). Secondly because she's bloody ugly; evne in life she must have been a real hag! Either a human mutant or perhaps a xenos.

The head was obtained when Karnak Zul led Castor to a remote temple on the shrine world of Torfal, Finial Sector. The temple was heavily defended by Sisters of Battle who unknowingly guarded the head of the Dusk Hag, placed there many centuries ago by an unknown Inquisitor or senior Ministorum official. Castor got to kill some whores of the Emperor and Zul got his head (Zul knew of it's location and nature because of his service to Inquisitor Renthor). Zul seems to think that the head can be 'reactivated' somehow, and that when that happens he'll be able to provide Castor with some really sage advice about the past, present and future of Calixis.