After Steve (Fred MacMurray) gets transferred in his job to California, the Douglas family sells their house in Bryant Park and heads for the West Coast. They soon realize that the people in California, including their neighbors, are as chilly as the weather is warm. Robbie (Don Grady) develops feelings for Katie Miller (Tina Cole), a girl at his new college.
It's the night before Robbie and Katie's wedding and everything that can go wrong does. First Tramp runs away and can't be found. Next the dressmaker sends the wrong gown and bridesmaids dresses to the Douglass house. Topping things off Robbie and Katie have an argument and decide to call the wedding off. Will Robbie and Katie get over their jitters and make it to the altar? Also, will anything else go wrong before the wedding?
The Douglas clan oversleeps on Robbie (Don Grady) and Katie (Tina Cole)'s wedding day and chaos reigns as they get ready. Meanwhile, Robbie's best man falls ill and Chip (Stanley Livingston) is recruited to take his place. Tramp is missing and arrives at the church just in time for the ceremony.
Katie learns that Robbie is buying her a gift for their four-week "anniversary" so she gets a waitress job to earn money to buy a gift for Robbie. As luck would have it, Katie has to fill in for the cigarette girl - skimpy outfit and all - the same day that Robbie's friend wins a free lunch at the restaurant. Naturally, Robbie blows his top when he sees how Katie is dressed, but Steve intervenes to patch things up between the newlyweds.
Ernie's new playmate, Mike, likes to pull childish pranks that upset the Douglas family. Robbie goes to talk to Mike's parents only to learn that Mike doesn't have a mother, and that Mike is actually a girl named Michelle! Unfortunately, Michelle's father treats her like his son rather than his daughter, only talking about sports and other "boy" things, so the Douglases try to bring out her feminine side.
Attractive lady engineer Eileen Talbot (Anne Baxter) is assigned to help Steve Douglas (Fred MacMurray) on a rush project in his office, and she applies her many talents to assure romantic, as well as technical success. Only level-headed Katie (Tina Cole) recognizes her as a manipulating female, long before the gullible male Douglases do.
Ernie (Barry Livingston) has innocently traded trinkets with two girls, and now they both assume that he is her boyfriend and will be taking her to the upcoming "Gym Dandy" school dance. Ernie doesn't want to go to the dance at all, and tries to get out of his dates, but each of the girl's parents insist that Ernie take their daughter to the dance. When both girls show up at the Douglas home the night of the dance, Chip (Stanley Livingston) steps in to escort one girl (Claire Wilcox) (who is thrilled to be with an "older man"), while Ernie escorts the other (Maureen McCormick).
While Steve (Fred MacMurray) is away on yet another business trip, and the rest of the men in the Douglas home are late returning from a sporting event, Katie (Tina Cole) is awoken by a late night storm and hears a loud, eerie, heart-beat sound, so she phones Steve in a panic. Everyone gets spooked when they learn the original owner died in the home, and it isn't until Steve returns that they figure out what caused the noise.
Chip's (Stanley Livingston) class uses a computer to match kids for dates, with kids from another school, for the upcoming "computer picnic". Chip is excited about his date (Eva Ein) - until he meets her and discovers that she's about a foot taller than he is. Chip is willing to go through with the date, but the girl realizes that Chip is very uncomfortable with the situation, and suggests that they call it off. So Chip and his buddies get together and swap their dates, based on more personal preferences, - pleasing Uncle Charley, who dislikes the newfangled computer dating. Chip ends up ...
Katie's (Tina Cole) snooty Aunt Cecile (Marsha Hunt) visits the Douglas home and clearly doesn't fit in - trying to make everyone act more refined and calling them by their given names. Luckily for Steve (Fred MacMurray), he's (surprise) headed out of town on a business trip. The rest of the family isn't so lucky, as now Cecile can stay over in Steve's room for an entire week.
With Katie now living with the Douglases, everyone finds that they are getting in each other's way a lot more often. Newlyweds Rob and Katie take the opportunity to move into a friend's apartment while they are away, but soon find that they miss what they had at home.
Chip is nervous about his upcoming driving test, so Katie asks Rob to teach her to drive so that she and Chip will be learning together. Katie has difficulties learning from Rob, and Chip wants to drive like a maniac while Steve is teaching him to drive like an old lady. Both eventually pass their driving tests and Steve lets each of them borrow his car - which returns with a mysterious huge scratch for which nether driver is willing to take the blame. Luckily, an honest kid comes along with his father to admit that he was responsible for the scratch, but the ...
After discovering that a neighbor (Dianne Ramey) has a cousin, visiting from Liverpool, who plays guitar, Chip (Stanley Livingston) invites the cousin to join his band, only to discover that he has a much more laid back, folk style than Chip assumed. But the new member (Jeremy Clyde of Chad and Jeremy fame) is just what the band needs, in order to win the top award at the local teen club.
Robbie and Katie serve as chaperones for a group of high school students, including Chip, on a trip. Much to Chip's consternation, Robbie manages to foil every plan they come up with to sneak away, including removing the car's rotor from inside the distributor so it won't start.
Katie (Tina Cole) becomes a tutor to earn some extra money and is surprised to learn that her first student, Craig Benson (Charles Robinson), is not only a male, but a handsome ex-boyfriend of hers. Robbie (Don Grady) doesn't mind at first, until he learns that the pair took a break from studying without his knowledge. A spat breaks out, and Robbie ends up sleeping on the couch, until both of the newlyweds realize they were partly to blame.
Katie complains that Uncle Charley is making her feel unnecessary in the Douglas home. Steve speaks to Charley who tries to makes amends by planning a rather bizarre "tea party" on Katie's behalf. Meanwhile, Chip volunteers for the school dance committee, but the otherwise all-female committee frustrate Chip by ignoring his ideas. However, the girls want to help out after Chip tells them what Uncle Charley is planning for the tea party - party balloons and donuts for dunking are out, scones, silverware and napkins are in. Much to Katie's surprise, the tea party turns ...
Uncle Charley buys an 11-year-old trotting horse, thinking of the potential purses that the horse could win. With Charley himself driving the sulky, the horse wins his qualifying race, but he discovers his horse's opponents were run-down nags more qualified for the glue factory than competitive racing. So Charley retires the horse at a friend's stable, where Ernie can ride him whenever he wants.
Robbie reports to camp for two weeks of military reserve maneuvers, and Katie decides to go along and stay at a nearby motel so that the newlyweds can be near each other. Meanwhile, Uncle Charley and the boys are camping at Yellowstone, which also happens to be close to Robbie's camp. During a stroll, Katie wanders into the mock battlefield and gets arrested by Robbie's unit. Later, each of the other family members try to locate Robbie and similarly get detained. Steve heads toward camp to prevent the family from interfering with Rob's duties, but he manages to get ...
Uncle Charley is in charge of Frolics Night at his lodge, but has trouble lining up the entertainment, so Charley joins in with his lodge brothers, dressing in drag for a chorus line number. After the show, Charley falls asleep and embarrassingly has to walk home in costume after waking up. While resting on a park bench, an elderly man mistakes Charley for a woman and begins flirting with him, and Charley gets arrested for hitting the man.
Steve is on a business trip to Amsterdam, Robbie is in the South Pacific for military reserve training, and Chip is on a school trip to Mexico, so Ernie and Uncle Charley are left home alone together. Charley invites an old shipmate, Toby, over for dinner, not realizing he's now a famous TV star that Ernie idolizes. Steve is stuck in his hotel room working, Robbie can't leave camp to visit the local town, and Chip gets tonsillitis and thus misses out on seeing Mexico, meanwhile, Toby invites Ernie and Charley to the television studio where there are filming - ...
The Wong family from Bryant Park drops in on the Douglases unexpectedly while on their way to Hong Kong. Since the hour is late, Steve invites the Wongs to stay overnight, forcing him to cancel the family camping trip planned for early the next morning. The Wongs are too polite to tell Steve that they have family in Chinatown who are expecting them, and Steve make his family promise not to tell the Wongs that they ruined the Douglases weekend plans.
Rob (Don Grady) and Katie (Tina Cole) invite a married couple - Denise (Lynn Loring) and Larry (Robert Dunlap) - over to the house, but instead of playing "immature" games suggested by Rob and Katie, Denise, a psychology student, insists that each person take turns telling the others what he or she dislikes about them. Rob and Katie are uncomfortable with the idea, and Denise criticizes Katie for her comments about Rob. Eventually, Larry gets fed up with Denise's antics, jeopardizing their marriage.
When Steve (Fred MacMurray) is promoted to head of the helicopter division, the secretaries snoop into his personnel file and are happy to discover that their new boss is an available widower. Uncle Charley (William Demarest) brings his helicopter-loving girlfriend Sally (Shirley Mitchell) for a plant tour, but when denied entrance, he tells his girlfriend Sally to pretend that she's "Mrs. Douglas", in order for her to get in. Meanwhile, Steve has invited Katie (Tina Cole) to visit the plant and tells her to let people know that she's "Mrs. Robbie Douglas". When the nosy secretaries see Steve with two different women ...
Chip is miffed when a friend steals his girlfriend. Ernie's friend Shorty - who has a movie date set for Sunday - can't go due to a prior commitment, so the girlfriend innocently asks Ernie to walk with her to the movies, since he was going anyhow. But Shorty believes that Ernie is stealing his girlfriend and can't be convinced otherwise until Shorty helps Katie in with groceries and Robbie pretends that he thinks that Shorty is flirting with his wife.
Ernie's friends convince him to sell two worn out tires found in the Douglas' storage room to get money to buy more powerful squirt guns, but Uncle Charley notices the tires are missing and files a police report. A guilty-feeling Ernie eventually confesses to the family about his "crime," and Steve takes it a bit further and makes Ernie go down to the police station to admit to what he did.