In the series opener, Mike Brady, a widower with three boys, marries Carol Martin, a widow with three girls. Just as the minister says "I do" the boy's dog, Tiger gets loose and chases the girl's cat through the wedding party. Chaos breaks loose which prompts Carol and Mike to yell at their kids to control their pets. Guilt over yelling at their kids comes into play later during Mike and Carol's honeymoon.

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.

Cindy has been cast as the fairy princess in the school play. She's excited that her mom and new dad will be able to see her in the production until she learns she can only invite one parent. Torn between who she should choose, Cindy fakes an injury to get out of being in the play.

No longer feeling needed around the Brady household, Alice makes up a story about an ailing aunt in Seattle in order to leave. Later the family finds out the truth and put "Operation Alice" in effect in an attempt to make her stay.

Jan comes down with a mysterious allergy and Carol and Alice try to determine just what is causing it. They deduce that the cause is Tiger, the family dog. Or is it?

With more and more of the girls belongings being moved over from storage, the boys become fed up and take to their 'No Girls Allowed' clubhouse in the backyard which sparks the first of many battles between the sexes. This leads the girls to try to build their own clubhouse.

When Cindy's doll, Kitty Karry-All turns up missing, she accuses Bobby. This leads to a mock trial with Alice as the judge to determine Bobby's guilt or innocence. Then later Bobby's kazoo turns up missing and he blames Cindy.