Warmaster is the ninth audio drama for the Horus Heresy Series that was not originally released as part of an anthology or other release. Warmaster was published online in December of 2012 as part of the Black Library's Advent Calendar 2012, on the 7th day. The audio drama was later republished in prose format as part of the Legacies of Betrayal main series anthology novel. This audio drama, along with several others were also released as part of the Echoes of Ruin audio anthology.
In the strategium of the Vengeful Spirit, Warmaster Horus sets up his assault on his father's Imperium. He discusses his brothers, Loyalist and Traitor, and his hopes and fears for the war he has begun... and whether or not he really thinks he can end it. But just who is Horus talking to as he lays out his plans for galactic domination?
- Warmaster (Audio Drama) by John French