Eleven hundred years after the apocalyptic destruction of the United States of America, peace between the remaining warring tribes has finally been achieved. Despite this peace, the Pelbar stronghold Threerivers retains its secretive and reclusive ways, keeping its distance from the other remaining tribes and guarding against change. A strict matriarchy, Threerivers remains the most conservative Pelbar community under the unquestioned and unyielding rule of its leader, Udge. Life in Threerivers continues without change until two young twin brothers, Brudoer and Gamwyn, accidentally initiate events that threaten the established order. The resulting chain of consequences sends Gamwyn on a quest to the far reaches of this postapocalyptic world. Within Threerivers, Brudoer's imprisonment threatens the long-established matriarchal rule of the Pelbar stronghold. The Fall of the Shell is the fourth book in the classic series of postapocalyptic novels about the people of Pelbar
