The Kindly Ones

Orestes was a cruel world, cold and inhospitable. Its first colonists were castaways from a crash landing, cling to survival through the institution of strict socio political pontrols. Over the generations life grew somewhat easier, but the code of honour remained. Misdeeds and errors were paid for with blood. At one time all miscreants were executed. Now a social death is imposed. Every Oresteian city has colony of "ghosts": ostracised citizens who must survive, somehow, without help from the living.
But galactic civilisation is spreading and Orestes is in its path. The old ways are under scrutiny. And though the Oresteian aristocracy will fight for the status quo, they have not reckoned on the power of a thousand ghosts.