The Shadowmasters is the seventeenth short story published in the Horus Heresy that was not originally part of an anthology novel. The Shadowmasters was originally published inside of the dust jacket for the hardcover edition of Corax: Soulforge. It was later released as an audiobook (MP3). It is also now included in the Corax anthology novel and in the Echoes of Imperium audio anthology. The cover art shown is from the audiobook edition, as the story was never released as a stand-aone e-book.