The Brady Bunch S01E02 - Dear Libby

An article in an advice column, Dear Libby, draws Marcia's attention. In the article, an anonymous person is in the same situation as Mike and Carol is in and this particular person is unhappy. This leads Marcia to draw the conclusion that Mike or Carol wrote the letter. She later shows the article to the other kids and they devise a plot to keep their newly formed family together.