Dark Angel renegade Moebius has tracked down the Green Knights' homeworld: Phagir, a world deep in the Hazeroth Abyss. The world was once home to human civilization, but now it is a wasteland, ravaged by strange, mutated lifeforms.

He's also found that the Chapter was stricken from Imperial records hundreds of years ago. As far as the Imperial war machine is concerned, they do not exist. The Knights themselves have long been sworn to Inquisitorial service. Currently they function as a sort of elite guard for the Maiden and her leaders.

Moebius has been tasked with trying to subvert the knights; they are of Dark Angel stock after all.