Anthony P. Kirby Sr. is a wealthy banker and businessman. He has just won a government munitions contract which will be very lucrative, especially if he can take out his number one competitor, Ramsey. To this end, he is buying up the land around Ramsey's factory in order to squeeze him out of business. The problem is, one property owner won't sell his home, holding up the plan. Kirby instructs his Realtor to make a larger bid, and if that fails, harass the homeowner until he sells.
Meanwhile, down in the basement, a discussion is taking place about the upcoming Fourth of July. Paul and Mr. DePinna want to sell their fireworks, and are trying to think of a way to advertise. Ed says that he could print up ads and put them in Essie's candy boxes when he delivers them, and this plan is enthusiastically adopted.
The affable judge reads the charges: disturbing the peace and manufacturing fireworks without a license. Grandpa explains about the commotion, and tells the judge that, if making unlicensed fireworks is against the law, they're guilty because they've been doing it for years. The judge dismisses the first charge, but fines them $1oo dollars for the fireworks. None of them have that kind of money, but all their watching friends pool their resources and pay the fine for them.
The judge then turns his attention to the Kirbys, saying that, as they were present, they too will be considered responsible unless they can give a creditable explanation for their presence at the Vanderhof's home. Mrs. Kirby refuses to allow Mr. Kirby or Tony tell what they were doing there, not wanting anyone to find out about Tony's interest in Alice. They are at an impasse until Grandpa takes pity on them and tell the judge that Mr. Kirby was there to see him about selling his house. This is too much for Alice, who angrily tells the judge the truth- that the Kirbys came to look her over to see if she was good enough to marry their son. Tony backs her up, and she turns angrily on him, saying that it's about time he spoke up, and that she's decided that it's his family who isn't good enough. At this point, the reporters manage to force their way into the room and start taking pictures of everyone. Confusion reigns as people mill about shouting, flashes go off, and Mrs. Kirby faints, landing on Tony which prevents him from going after Alice as she darts from the room.
In the end, all is well. Once again, the family gathers around their table for dinner, the Kirbys, having sold them back the house, joining them. Mrs. Kirby looks a little unnerved, but is gradually starting to enjoy herself. Grandpa stands and thanks God for their family and all that they have, and the movie closes out with them all heartily eating and talking animatedly over top of each other.