Nathaniel Garro, knight errant and agent of the Sigillite, returns from the battlefields of Calth to find a new mission already waiting for him - a ragged fleet of Space Marines from several Legions lingers at the edge of the Terran system. With the presence of World Eaters and Emperor's Children causing concern among the loyalist defenders and drawing a grim parallel with his own frantic flight, Garro must look beneath the obvious if he is to determine friend from foe....