Curtis (Gale Gordon) comes back from a Hawaiian vacation with the intention of moving in with his son, Ted, and his family. He arrives just in time to learn that his son's mother-in-law, Lucy (Lucille Ball), Curtis's new business partner, has moved in with the family. Crotchety Curtis is annoyed that not only does he have to put up with her shenanigans at work, but now at home as well.
John Ritter is doing a play in town, and stops into the hardware store for some antique doorhandles. But instead of being helpful, Lucy is hurtful -- she advertantly injures his hands and foot. So Lucy insists that John stay with her. After the lead actress drops out of the play, Lucy talks John into offering her the part of his love interest.
A former flame of Lucy's, who is a business prospect for Curtis, comes into the store. After he takes her out, Lucy decides that she does not share the same feelings for him that he has carried for her.
When a talk-show host comes into the store, Lucy talks him into inviting Curtis on for a Mr-Fix-It segment. Curtis reluctantly agrees to let Lucy join him, at the urging of Becky. But while gluing a lamp together, Lucy ends up gluing herself to Curtis. . .and both talk show hosts!
While looking for things to put in the yard sale, Lucy happens across her old saxophone and encourages Becky to take up playing. However, Becky finds playing the instrument unsatisfying, as does the annoyed Curtis.
Lucy and Curtis get a computer to help with the books at the store. When she uses it to order a non-returnable fleet of merchandise, Lucy tries to get the bank to stop the check -- and accidentally misinforms them that Curtis has died.
While trying to pass off a Kevin's teddy bear as her own during a clean-up sale, to help avoid taunting from one of Kevin's friends, she sticks it in a bag. The bag is then purchased with the bear inside, so Lucy puts up reward posters around town. When the woman comes in to pick up the reward, she's asking for a lot more than the $50 that Lucy is offering.
Lucy's sister Audrey comes to town just in time to see Margo and Ted renew their vows. Lucy's excitement is diminished when Audrey starts making all the wedding arrangements, resulting in a cake fight between the two siblings.
After the hardware store is burglarized due to Lucy foolishly leaving a key in a rock outside, she has the brilliant idea to get a goose to guard the store. But the goose never gets a chance to terrorize the burglars -- he's too busy terrorizing the store's owners.
Ted and Margo feel that Curtis and Lucy are spoiling their grandchildren too much. It doesn't help matters when Curtis begins building Kevin a treehouse, which begins a quarrel between the couple. While working on the treehouse, Lucy and Curtis decide to relieve Ted and Margo's burden by arguing over which will move out -- and Kevin walks off with the ladder, trapping them in the tree.
When Lucy makes health shakes for the family, they show their appreciation by pouring them each into an ailing plant. When the plant shoots up overnight, Curtis thinks he has a million dollar plant growing supplement -- but Lucy can't remember what she put in it.
Curtis sells Lucy his share of the store so he can retire. Lucy goes all out for a solo-ownership celebration and winds up nearly broke. So she interviews candidates to take over Curtis' position, finally settling on Curtis -- who found retirement less satisfying than he had expected.
Lucy, jealous that everyone else in the family has a trophy to boast, is urged by Becky to join a talent show. After trying her hand at singing, dancing, telling jokes, and doing magic, Lucy finally settles on reciting a song. When she fails to win the trophy, the grandkids get her one of her own that reads "World's Greatest Grandma."