When Harold Hill (Robert Preston), a traveling con man, arrives in River City, he convinces the locals to start a band by purchasing the uniforms and instruments from him. His intention is to flee as soon as he receives the money. Librarian Marian Paroo (Shirley Jones) suspects Harold is a fraud, but holds her tongue since her moody brother, Winthrop (Ronny Howard), is excited about the band. As Harold begins to develop feelings for Marian, he faces a difficult decision about skipping town.