When Shirley Partridge goes into her garage to find out what all the noise is about, she discovers her children: Keith, Danny, Chris, Tracy and Laurie warming up for a song which they have collectively written. In need of a soprano to round out the harmony, the young Partridges' volunteer their mom and, to the whole family's surprise, the song sounds alright. As a matter of fact, it sounds terrific. On his own initiative, Danny Partridge tape records their terrific tune and seeks out a business manager's ear. After trailing a big-time manager (Reuben Kincaid) all day, he finally gets him to listen to the tape. Reuben is reluctant to promise too much, but he promises the Partridges he'll give their song a fair "hearing". Within weeks, the garage-inspired song becomes an instant hit and overnight the Partridges are in demand throughout the country.
Shirley Partridge is uncertain how to adjust to their sudden success. A recent widow, she could certainly use the money. She decides that she's going to take her family on the publicity tour. She repaints an old school bus (which she almost knows how to drive) and thus, the Partridge Family begins to ride the road to success. Their first stop, Caesar's Palace in Las Vegas. After an introduction by Johnny Cash, Shirley is somewhat shocked to find all five kids suffering from a bad case of stage fright. She coaxes her children out of their silent trance by having them pretend to be back home in the garage. They finally begin to play and eventually earn a standing ovation. They've come a long way from their garage.