The Watcher (Audio Drama)

The Watcher is the twenty-seventh audio drama for the Horus Heresy Series that was not originally released as part of an anthology or other release. The Watcher was published in December 2014 by the Black Library as part of the Black Library's 2014 Advent Calendar, on day 24. The title was later published in prose format as part of "The Horus Heresy Quick Reads Subscription" week on February 26th 2016, and again as part of The Silent War main series anthology novel.

Official Synopsis
A shuttle returns to the Sol System bearing the sole survivor of a traitor attack – however, delirious and so close to death, his tale remains untold. Ison of the Knights-Errant, formerly a Librarian of his Legion, delves into the mind of the warrior, and the truth of it will chill him to the core...