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.

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.