Mame Dennis, a progressive and independent woman of the 1920s, is left to care for her nephew Patrick after his wealthy father dies. Conflict ensues when the executor of the father's estate objects to the aunt's lifestyle and tries to force her to send Patrick to prep school.

Traveling con artist Harold Hill targets the naïve residents of a small town in 1910s Iowa by posing as a boys' bandleader to raise money before he can skip town.