Grandma and Grandpa come to the Partridge house having rediscovered themselves, or so they think, through an experience with an encounter group. In an effort to share what they lerned with Shirley and the kids, the grandparents provoke them all into expressing their hostility toward each other so that their pent-up feelings will be brought out into the open. When the kids start arguing bitterly, Shirley is forced to tactfully suggest to her parents that they are interfering with her family life, and they leave. A few days later a tearful Grandma comes knocking on the Partridges' front door, explaining that she and Grandpa had been too honest with each other, for he had said that their marriage had no zip to it. Grandpa later arrives and they consider first getting a divorce and then living together as a means of revitalizing the marriage. Instead, they take Shirley's suggestion to pretend that they are divorced, and then go out with other people. (thetvdb.com)