Complex sentence: A corrupt, icy official in the Roman Catholic Church who keeps a mistress--not uncharacteristic of the time--he has arranged a spy (Bosola) to spy upon his sister-all this on the quiet, however, leaving others ignorant of his plotting.
Split into simpler sentences: A corrupt, icy official in the Roman Catholic Church who keeps a mistress--not uncharacteristic of the time--he has hired a spy to prey upon his sister. All this on the quiet, however, leaving others ignorant of his plotting.