An omnibus edition of Fifth Business (1970), The Manticore (1972) and World of Wonders (1975). The books, noteworthy for their faultless prose, memorable characters and trenchant humor, follow the fate of three youths from Deptford, Ontario. Fifth Business is the most straightforward, the memoir of headmaster Dunstan Ramsey and among our favorites. In the Manticore Davies sidesteps into the world of Jungian analysis, a puzzling book. World of Wonders, starring Magnus Eisengrim, is magical.  (CND223, $22.00)