Subterfuge proves to be the order of the day in the Nurthene campaign, as it is discovered that a Xenos-augmented Human spy is loose in the theatre, attempting to orchestrate the complex plans of his ans that included the manipulation of events that resulted in the Alpha Legion arriving on Nurth. It becomes evident that the Alpha Legion do not operate as other Astartes Legions they make great use of subterfuge, so much so that the Lord Commander was not aware of their presence and contribution to the campaign until they announced themselves. The Nurthene rebellion is doomed as a result, the majority of their armed forces bottled up in an enormous siege.

Astartes of the Alpha Legion, led by their Primarch, are tasked to the theatre. Tired and stung by this turn of events, Adeptus Astartes reinforcement is requested, and granted. Despite the leadership of the particularly prestigious and accomplished Lord Commander Teng Namatjira and the presence of ancient and elite Imperial Army regiments, the native inhabitants seem to be holding off the Imperial forces with relative ease. The Compliance Action on the world of Nurth is not going smoothly. But what drives the Alpha Legion? Can they be trusted, and what side will they choose when the Great War begins? Loyalties are put to the test, and the cunning schemes of an alien intelligence revealed. The Space Marines of the Alpha Legion, the last and most secretive of all the Legiones Astartes brotherhoods, arrive on a heathen world to support the Imperial Army in a pacification campaign against strange and uncanny forces.

A Great War is coming, and it will engulf the Imperium of Man.

Horus heresy book 7 inferno