The television panel game What's My Line? became an American favorite in the course of its 17-year-long run. Aired on CBS from February 2, 1950 through September 3, 1967, it remains the longest-running show of its type in prime-time television history, having seduced viewers with a premise both rudimentary and clever. Contestants with uncommon occupations first signed their names on a blackboard, and then whispered their "lines," or professions, to master of ceremonies John Daly and the viewers at home. Next, four panelists queried the contestants in order to ascertain their professions. Questions could be answered only with a simple "yes" or "no." For each "no" response, a contestant earned $5; after ten negatives, the game ended with the contestant pocketing $50. One participant each week was a "mystery guest," an easily identifiable celebrity. Here, out of necessity, the panelists donned masks, with the contestants responding...