The Movie: Meredith Willson's tuneful score has made this a landmark American musical. As the leading lady, Shirley Jones radiates wholesomeness (perhaps because she was secretly pregnant at the time).
Before the Kiss: Robert Preston's Professor Harold Hill is a con man posing as a band leader. He's used to swindling towns and seducing spinsters until he meets Marian the librarian (Jones).
After the Kiss: A life of crime loses its charms when you meet the right woman. Since the town boys can now somehow play "76 Trombones" without one legit lesson, perhaps it's worth sticking around and getting married.

The Music Man, Shirley Jones and Robert Preston, 1962. Photo courtesy of the Everett Collection.