Ferrus Manus: The Gorgon of Medusa: Primarchs: The Horus Heresy, Book 7 (Unabridged‪)‬

The Great Crusade has swept across half the galaxy, a million human worlds now embracing the truth and reason that comes with allegiance to the rule of Terra. But even such unparalleled success comes at a cost. 

Rumours abound that the Emperor plans to step back from the Crusade and raise one of his primarch sons to lead in his stead. Faced with the bitterly noncompliant human empire of Gardinaal and a leaderless host of Ultramarines, Thousand Sons and Emperor’s Children at his Legion’s command, the Iron Hands primarch Ferrus Manus decides to make an example that even the Emperor cannot ignore.