This work covers nearly 300 syndicated radio mystery and adventure serials that aired in the early or middle twentieth century. To be included in the book, a series must have included one or more characters who regularly appeared in occupations or avocations that fought against espionage, theft, murder, and other criminal activities. Each entry includes the name of the series, air dates (stations and times are noted), the sponsor, extant episodes, cast information (such as the directors, writers, composers, announcers, lead actors and supporting actors), and a brief synopsis.