Magisterium (Black Library Advent Calendar 2017 #7)

Devastated from the Webway War, the remnants of the Custodian Guard prepare for the coming of Horus. But as they rearm and adapt to their changed circumstances, conflict brews with the Imperium's Lord Commander…

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…