These Boylston books have won a substantial following, and this one -- like its predecessors -- is lively and entertaining, a harmless success story. Two 18-year old New England girls in search of a stage career are good sports and take in their stride a variety of experiences with booking agents, producers and radio directors. There is no central plot theme, just a series of episodes, some success, many disappointments, and a cast of characters of the theater which wiIl appeal to stage struck girls.