Returning from the battlefields of Calth, Nathaniel Garro, Knight Errant and agent of the Sigillite, finds that a new mission awaits him - a battered fleet of Space Marines from several Legions, located on the edge of the Terran System. With the presence of the World Eaters and the Emperor's Children causing wariness among loyalist defenders, and the grim parallels drawn to his own tumultuous flight, Garro must look deeper, beneath the surface of the obvious, if he is to discern who is friend and who is foe...