Knighted in 1911 for distinguished service as a British foreign officer, hanged five years later for high treason to the Crown, Roger Casement is one of the most enigmatic figures in the long history of troubles between England and Ireland.  His true character has been a source of mystification and of passionate contention.  This new biography, which never loses sight of the suffering human being behind the roles ascribed to him--martyr, traitor, flawed hero, moral degenerate--offers a vivid, compassionate, and conclusive analysis of Casement and of his career.   Born in 1864 in Dublin and reared in County Antrim, Roger Casement very early developed an obsessive love for Ireland.  After years of consular service for England and after being knighted for his effective campaigns against brutalities inflicted upon tribesmen of the Congo and the Amazon, he resigned to dedicate himself to the cause of Irish freedom.   B.L. Reid narrates with mounting drama and tension the events leading to Casement's participation in the Easter Rising of 1916, and his subsequent arrest, trial, and execution.  It becomes clear that in a sense Casement engineered his own destruction.  A strikingly handsome and romantic figure who had been much admired for his humanitarian public service, Casement went to trial with powerful support for a plea of clemency.  This support evaporated, however, when his notorious "Black Diaries," which recorded in detail his life as a homosexual, were circulated by British officials.  Although many Irishmen denounced the diaries as British forgeries, Casement went to the gallows.  A controversial figure to the end, he was raised to the pantheon of martyred political heroes in Ireland, while in England Madame Tussaud featured him in her Chamber of Horrors.   Through close study of Casement's diaries Mr. Reid demonstrates that they are authentic, that they fit into the total picture of a symptomatic modern man--passionate and courageous, yet deeply divided and confused.