THE MASK OF APOLLO by Mary Renault. 371 pages. Pantheon. $3.95.
Mary Renault's appreciation of the glory that was Greece has produced three fine period novelsThe Last of the Wine, The King Must Die and The Bull from the Seaeach fondly flavored with enthusiasm and scholarship. In this fourth reconstruction of the Hellenic past, she grapples with the ordeal of Dion of Syracuse, who tried vainly, 24 centuries ago, to convert a tyranny into Plato's ideal city-state. This theme does not easily catch the modern fancy; after all, the roll of centuries has only emphasized the unattainability of Dion's dream. It appears...