It's mutual love at first sight for Mother and wealthy Conrad Byron who offers to trade him limousine and chauffeur for Dave's car.
A collision with a truck leaves Mother with amnesia and Dave with a problem, how to bring back a car's memory.
When Dave neglects to set the parking break after parking on a hill, Mother rolls into an open van that is bound for Mexico.
As Dave drives up the mountains, Mother gets higher and higher from the alcohol in her antifreeze.
Dave gets back at his neighbors who are petitioning him to get rid of his antique eyesore by starring the car in a TV commercial.
While driving the kids to camp, Dave is stopped by a sheriff who asks him for his driver's license and discovers that it has expired.
Mother is furious when she learns that Dave intends to let Barbara choose her own Christmas present.
Dave's mother in-law arrives for a visit and it's soon apparent that there is one mother too many on the scene.
After being married for 8 years, Barbara and Dave decide to go on a honeymoon. However, Barbara's mother, an astrology nut, warns them of impending danger.
Lawyer Dave Crabtree's troubles begin with the purchase of a decrepit 1928 Porter that claims through the radio to be his mother.