No one believes Ernie when he says that he saw a flying saucer, so he returns to the site with his camera and takes photographs. After Steve gets them developed, he immediately takes the photos to the government where it is explained that Ernie saw a new top secret Air Force project that went awry, but Steve isn't allowed to tell Ernie any of the classified details.
A new family moves in next door to the Douglases - a widowed mother and her three children, plus "Aunt Maude". Robbie (Don Grady) and the daughter Peggy Snell (Jackie DeShannon) get along swimmingly, but the rest of the family members are at odds with their next-door-neighbor counterparts. Robbie is caught in a Romeo & Juliet romance, until he and Peggy set Shakespearean dialog into modern songs and play them for the families.
Robbie and Steve nearly forget that trout season starts on Saturday which means it's time for their annual fishing trip together. One problem: Robbie hates fishing, but is apprehensive about telling his dad, who loves it. Meanwhile, new family member Ernie is all to eager to go along, but Steve tells him his chance will come some time in the future, after Chip - who also hates fishing - gets his chance. Ernie learns that he is considered a true Douglas family member because he can wait his turn.
Ernie's friends brag about the athletic abilities of their fathers, and agree to compare sports trophies that their fathers have won. To Ernie's dismay, the only trophy he can find is for debating. The kids then decide that all the fathers will compete in a 2-mile cross country race on Saturday. Steve would rather compete in bridge or playing the saxophone, but agrees to race. It turns out that all the fathers are now out of shape, and Ernie understands when Steve lets another man win the race since his son needs the boost in self esteem more than Ernie.
Robbie has aspirations of becoming a bullfighter. He starts out by confronting a killer bull with no knowledge about the sport whatsoever. Then, after a few lessons, he tries out his skills on a farmer's pet bull, who is tame, completely harmless and disinterested.
Anticipation is high as Robbie prepares to ask the exchange student he's fallen in love with to marry him. Unfortunately, Robbie discovers that his friend popped the question the night before, and she accepted.
Chip's class has a school dance with an olden day theme. The students are to ask one of their parents to attend with them. Since Chip does not have a mother to take, he takes his father who is matched with Chip's date's mother.
Steve is dating Natalie, who has a teenage age daughter Melinda. Chip does not like Melinda as she seems pushy. He pretends to get along with her so that his father has an easier time when dating the mother.
Charley goes to Ernie's class and tells tales of his days of being a seaman. He exaggerates a bit, and the teacher falls in love with the romance of the story. She quits her job and asks Charley to marry her and travel to Pango-Pango.
To Ernie's dismay, Steve refuses to help him with his school science project. All the other kids have their parents help them and create better projects, but Ernie is the only one who ends up learning anything.
When Ernie invites a vagabond that he befriended in the park to the house for dinner, Steve decides to not pass judgment and give Ernie the chance to realize that the guy is nothing more than a freeloader.
To Steve's dismay, Robbie quits school since he has been making money hand-over-fist by working for a friend's real estate company. Robbie gets a real education when a torrential rain storm reveals that the home he is showing has hidden flaws.
Uncle Charley gets reacquainted with an old merchant marine shipmate who invites Charley along on a sea voyage. Charley wants to go, but realizes the Douglas family needs him. The family sees that Charley wants to go, so they pretend that they are fully capable of taking care of themselves.
Steve's company sends him on a business trip to Japan and includes the entire family for an all-expenses-paid vacation. Charley reminisces about his merchant marine days, and the girl he left behind in Honolulu. Charley has forgotten that she has aged quite a bit since he last saw her, and after they meet he does all he can to avoid her. Meanwhile, Robbie runs into a girl he knew back home.
After Steve 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 develops feelings for 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 and Katie's wedding day and chaos reigns as they get ready. Meanwhile Robbie's best man falls ill and Chip 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 is assigned to help Steve Douglas 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 recognizes her as a manipulating female long before the gullible male Douglases do.
Ernie's 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 steps in to escort one girl (who is thrilled to be with an "older man"), while Ernie takes the other (Maureen McCormick).
While Steve 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 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 class uses a computer to match kids with dates with kids from another school for the upcoming "computer picnic." Chip is excited about his date - 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 trading dates...
Katie's snooty Aunt Cecile visits the Douglas and clearly doesn't fit in - trying to make everyone act more refined and calling them by their given names. Luckily for Steve, 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 has a cousin visiting from Liverpool who plays guitar, Chip invites him 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 & 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.