"Music and girls are the soul of musical comedy," one critic wrote, early in the 1940s. But this was the age that wanted more than melody and kickline form its musical shows. The form had been running on empty for too long, as a formula for the assembly of spare parts—star comics, generic love songs, rumba dancers, Ethel Merman. If Rodgers and Hammerstein hadn't existed, Broadway would have had to invent them; and and came along just in time to announce the New Formula for Writing Musicals: Don't have a formula. Instead, start with strong characters and atmosphere: murderous romantic triangle set against a frontier society that has to learn what democracy is in order to deserve it; or dysfunctional family seen in the context of class and gender war. With the vitality and occasionally outrageous humor that Ethan Mordden's readers take for granted, the author ranges through the decade's classics— . He also covers illuminating trivia—the spy thriller , whose star got so into her role that she suffered paranoid hallucinations and had to be hospitalized; the smutty , damned as "burlesque with a playbill" yet closing as the longest-run musical in Broadway history; , in which Mary Martin and Nancy Reagan were Chinese; and the first "concept" musicals, . Amid the fun, something revolutionary occurs. The 1920s created the musical and the 1930s gave it politics. In the 1940s, it found its soul.