Black Oculus is a short story published in the Horus Heresy Series. Black Oculus was originally published simultaneously as a part of the anthology novella Blades of the Traitor and as a stand-alone e-book. It is also now also included in the War Without End anthology novel. Black Oculus is the sequel to Book 23, Angel Exterminatus and is the beginning of the Battle of Tallarn story arc of the Horus Heresy.