Grandma Dowdel's small town is getting ready to celebrate its centenary, or hundredth anniversary. As one can imagine, this is quite a big deal and lots of people are excited about such an historic event. Joey and Alice certainly are; they've entered into the swing of things by dressing up in old clothes. To be precise, they dress up in, respectively, their late grandfather's wedding suit, and Grandma Dowdel's wedding dress.
As for Grandma Dowdel herself, she's none too enthusiastic about the Centennial celebrations. One of the reasons for this seems to be her antipathy towards Mrs. Weidenbach, banker's wife and member of the committee organizing the town's celebrations. Mrs. Weidenbach wants Grandma to get involved, but she's not interested.
However, she is prepared to put one over on Mrs. Weidenbach by depriving her father of the Oldest Settler prize at the forthcoming Centennial celebrations. To that end, Grandma heads off with the kids to Uncle Grady Griswold's place. Uncle Grady has reached the ripe old age of 103, and Grandma is certain that this makes him the oldest settler in town. She hopes to “borrow” him for the Oldest Settler contest, where she hopes he'll beat Mrs. Weidenbach's father, who, as a ninety-year-old, is a spring chicken by comparison.