Magisterium (Short Story)

Magisterium is the sixty-third short story published in the The Horus Heresy series that was not originally part of an anthology novel. Magisterium was first published on day 7 of the Black Library's 2017 Advent Calendar.

Synopsis
The Webway War is over, the Custodian Guard devastated by the daemonic hordes that flooded the lower reaches of the Imperial Palace. Constantin Valdor, commander of the Emperor's Guard, stands at the head of his fellows, but in conflict with the Lord Commander of the Imperium, the Primarch Rogal Dorn. And it is not the first time Valdor, the Emperor's Magisterium, has found himself pitted against a Primarch. His memories of Prospero are all too fresh…