Girls Under 21: Francis Ryan, living high-and-free-wheeling life as the wife of gangster "Smiley" Ryan, spends some time behind bars as a result of her husband's activities, and, when she gets out, realizes she has been a bad example for her kid-sister, Jennie White, and five of her friends. With the aid of her old boyfriend, she manages to divert them from their juvenile-delinquent path leading to disaster for each.