A Missile launch, sleeping in and Daylight Saving make for an interesting Monday morning. The Douglas household is a chaotic affair of lost indian arrow heads for Chip's turn in show and tell at School, Robbie's missing trumpet and some important lost plans of Steve's that Mike has nearly burned in the incinerator.

The day -- or rather the night -- of the big event finds expectant mother Katie quite calm, and Steve and Uncle Charley quite the opposite, and a hapless father to be off on Army manouvres. At the hospital, Katie gives birth to identical triplet boys and Steve must adjust to the fact that he is a Grandfather, three times over.

Thanksgiving Day's turkey dinner is threatened when the electricity is short-circuited throughout the neighborhood. Chip decides to bring along his Indian friend as his sole guest much to the annoyance of his brothers who say he is a bum who lives near the railway tracks in a rundown old shack.

Ernie's adoption into the all-male Douglas household is threatened by a regulation that there must be a lady of the house. Steve again makes a request to adopt the child, but Misses Coulter and Miller of the adoption agency, say they are powerless to change the regulations. Miss Miller has a brilliant idea, however, and soon the family is appearing before a judge who decides that housekeeper Uncle Charley can legally be designated the 'lady of the house'. Charley approves if this fact is kept secret and Ernie is enthusiastically welcomed into the family.

The usually all-male Douglas household becomes a refuge for an attractive girl dancer who has been evicted from her apartment, when Steve attends an office stag dinner. He takes her home where he lends her some of Robbie's clothes.

Steve Douglas takes his family to his birthplace of Bedford Springs. He tries to locate his 1940 fiancee Ellen, married and still living in town, but he is disenchanted by the changes in her. Still pretty, she lives with her obnoxious husband and ill-mannered children.

Chip begins studying with a pretty co-ed whose disciplinarian father wants to know why her new friend is spending so much time with her. Meanwhile, on the eve of Steve and Barbara's first wedding anniversary, Dodie announces she is throwing a surprise party, but neglects to tell everyone when or where.

The town of Bryant Park takes sides violently when it is proposed to cut down the tree which stands outside of Robbie's girlfriend's home. The Douglas family are soon involved as Bub joins a women's group in the neighborhood to save his favorite tree from being torn down.

Steve Douglas gets a parking ticket from Robbie's girlfriend, a pretty meter maid, and another citation for not having his driver's license renewed -- and then flunks his driving test. Soon Robbie realizes that he's given his father last year's manual to study and that some laws have been changed.

Robbie's science master announces a special achievement award for being a straight 'A' student and to his embarassment, Robbie wins it. This causes more trouble than he could have imagined but Steve does his best to assure Robbie that he did deserve the award.

The family is excited when Steve might travel to Hawaii on business, but there is dismay on their faces when the 'For Sale' sign goes up outside 837 Mill Street. Going on a trip to Hawaii is one thing, but could the entire family pack up and move there?

Mike and Sally finally get married and leave for the East where Mike has a job as an assistant college psychology instructor. Robbie happily moves into Mike's old room. When Uncle Charley notes that they may soon be calling Steve 'Grandpa' he becomes somwehat concerned about growing old and calls up his former girlfriends. Robbie, now a college man, offers to help his father make friends with younger women, and while pretending to be disinterested, tries a few of his suggestions. When it is learned that Ernie must return to an orphanage, because he will not be allowed to accompany his foster parents in their move to the orient, Chip invites Ernie to move in permanently, giving Steve three sons once more.

Steve explores the possibility of adopting 10-year-old Ernie but runs into antagonism from Uncle Charley, who can forsee nothing but more work with a new boy to take care of. The family desperately wants to adopt the boy and Robbie decides that Steve must make a play for the lovely Miss Coulter. Her boss comes to inspect the house just as the boys have made a shambles of the place. At eight the next morning, Miss Miller returns. She inspects the house, spic and span now, and ushers in a happy Ernie, who is to stay on a temporary basis.

When Chip adopts a Beatle-style, shoulder length haircut, the other members of the family feel that Steve should lay down the law to the long-haired one, but he and his associate consult a company psychologist for a solution. Steve decides not to be a strict father but to give the boy more attention, without affect.

The Douglas family returns from a trip to Britain and as the family watches home movies of their vacation, the amateurish footage reveals the reason for Steve's current moodiness: He is still carrying a torch for a lovely widow.

The contractor that Steve hires to add a baby alcove to Robbie and Katie's room leaves much to be desired. He displays all the charm of a top sergeant and is putty in Katie's hands, but is exasperatingly gruff and non co-operative to the males in the Douglas home.

Barbara's natural enthusiasm bubbles over into an embarrassing evening for Steve and some of his business associates. Barbara explains to Steve that adrenalin gets her going in competition, and she is apprehensive when he is asked to play in his work's bowling team for fear she will make him lose concentration.

Robbie's new girlfriend offers to get him and his guitar an audition at a club, and introduces him to a strange new world of far out youngsters who comprise the audience. When Robbie becomes a smash his family struggles to bring him back from stardom.

Barbara is flustered when she receives a phone call from a former college suitor, and is very apprehensive when Steve invites him to dinner. The entire family is anxious to meet her old flame, thus compounding her uneasiness.

Aeronautical Engineer Steve Douglas and his youngest son Chip face a parallel problem -- how to rid themselves of two designing females.

Unaware of each other's problems, Steve and Robbie engage in what seem to be widely varied projects. Robbie is trying to construct a race kart and Steve is in a rush to help a missile manufacturer get his project off the launch pad in a race to beat a rival company.

Steve gives Mike advice on love after he announces his passion for his new girlfriend Darlene, who Mike wants to devote time to, so he hardly welcomes Steve's suggestion that he help find a date for the girl in his office.

Chip and his new sidekick Ernie find some old treasure maps but get lost in the woods when they go treasure hunting, causing the family's plans to be changed when they have to go looking for them.

Robbie's glamorous girlfriend invites him to the exotic Brookdale Country Club, and he resolves to put pressure on Steve to join, despite the fact that his father isn't much of a joiner.

A huge shaggy stray dog adopts Steve Douglas and disrupts the neighborhood with his howls when Steve tries to leave home. A neighbor and lover of stray animals, is delighted to learn that Steve plans to keep the dog until its owner can be found, rather than sending it to a shelter. However, the dog continues to regard Steve as his mother as well as his master.