Mary is going away to a new college in the fall. As part of her leaving, she is putting on a "large" outdoor formal party that will be in the backyard. At the same time, Jeff is flirting, yet again, with car ownership. Jeff has $189 saved to purchase his vehicle and plans on getting a great deal by attending a City of Hilldale held auction, where the city sells old vehicles. At first Dr. and Mrs. Stone are reluctant, but Jeff agrees to be responsible for the car and will pay for the insurance, gasoline, maintenance (tune-up, fixing, oil), etc. Finally Dr. Stone agrees.
As Mary, Mrs. Stone, Dr. Stone, and even Trisha are working on the upcoming party, Jeff returns home with not a car, but an "Hilldale Bus Lines" bus. He plans on making money in various ways. Besides driving people to away football and basketball games, he plans on charging kids $.10 a ride ($.20 round trip) each to ride to school, instead of walking. The bus can hold 50 kids about the size of Trisha and thus have an income of $10/day.
While Jeff was able to drive the bus home, later in the day it won't start for Jeff, when he is wanting to go to school. When Jeff says he has enough time left and is going to work on the bus, Mrs. Stone tells him to go off to school now. Mary wants the bus out of there and has some of her college friends come to fix it. While they are trying to fix it, Trisha plays at being a bus driver even down to wearing a bus driver cap. When her friends give up after several hours, Mrs. Stone has a two word solution: "Tow Truck."
A two truck arrives, when the driver tries to lift the bus up, the weight of the bus lifts the two truck up by the front (engine and all). The driver and Mary's friends are unable to unhook the two vehicles. They attempt using a pick up truck to lower the two truck with even worse results, as it becomes stuck with its rear up in the air. All the while Trisha is spinning around and playing, as though, this situation is all of big adventure.
Finally, they're able to unhook the tow and pick up truck from the bus, but can't move the bus. Mary and Mrs. Stone sit on the hallway steps to the second floor trying to figure out what to do. Mrs. Stone says they must figure out how to turn a disadvantage (the bus) into an advantage. and with that she has an idea.
She moves the party from the backyard to the front and decorates up the bus a "College Special." Everybody loves the bus idea and it clearly is a hit and even into the next day people are talking about the marvelous bus at the party. The episode ends with Dr. Stone suggesting Mary give Jeff his share of the honors for the great party.
Jeff returns from going downtown with news that the city will be by to pick up the bus in the afternoon. He traded the bus for a police car that, unfortunately, has a short in the wiring that cause the siren to go off at the wrong time, such as when no one is in the car.