Having received a catalog of silver anniversary gifts in the mail, the Jones children, Jack, Roger, Lucy and Bobby, try to decide what to buy for their parents' anniversary with the twenty-three dollars they have saved for the occasion. Before they can decide, their parents, Louise and John, come in. When Bobby, the youngest child, accidentally shows the catalog to Louise, she and John reminisce about their engagement. They honeymooned in Niagara Falls rather than Europe because John used the money to buy his drugstore. Presently, a phone call from Warren Baxter, a banker, interrupts them, and John leaves to meet Baxter, who tells him that the Delta Oil Company is offering $5,000 for some property John owns. John agrees to the deal and tells Baxter that he is going to use part of the money to take Louise on an anniversary trip to Paris Falls to do some trout fishing. A bank teller, who overhears, misunderstands and spreads gossip that John, who is also the city's mayor, is taking his entire family to Paris. The news reaches John's mother Granny and Louise before John arrives home. Not realizing the situation, John is shocked by the children's excitement until Granny explains it to him. In private, she talks John into going through with the trip. On the boat, Jack meets Marguerite, the daughter of Countess Varloff. In Paris, John's cousin Willie meets the family with a fully-planned itinerary. That evening, while everyone is out, a maid sees some of the photographs of artillery that Roger has taken during his sight-seeing tour and reports to the house detective Emile that the Joneses are spies. Meanwhile, at dinner, Countess Varloff's boyfriend, Monsieur Duroche, sends a note to Marguerite saying that Jack will do and that they should be at the La Cresse airfield at dawn. In the middle of the night, Jack, who has experience as a pilot, sneaks out of the hotel with his flying helmet to meet Marguerite and Duroche. In the morning when the family awakens, they discover that Jack has disappeared but find the note from Duroche, which leads them to the airfield. Emile, posing as a hotel waiter, overhears the entire thing and reports to France's intelligence agency. The handwriting on the note is identified as that of Duroche, a dangerous spy. Air force planes are deployed to force the plane down. When it lands, plans of a sector of border fortifications are found in Jack's suitcase, and he is arrested, along with the countess and Duroche, for the theft of the plans. Jack is released after he informs the police that Marguerite asked him to fly her and Duroche to Switzerland to obtain help from her uncle because the countess and Duroche were attempting to force her to marry Duroche. When the family returns to the hotel, they find the manager, who believes them to be spies, removing their luggage in lieu of payment for their as yet unpaid bill. John pays him almost $3,000, which is most of the money he has left. The hotel manager then gives a commission to Willie, who arranged their stay at the hotel. Although Willie does not want to accept it, John orders champagne, caviar, pate and pheasant, and puts it all on Willie's tab.