In Palm Beach, Florida:

In his pursuit of Gerry to West Palm Beach, Tom meets the arrival of her train and speaks to the black porter. He is told that she lost all her clothes and disembarked at the Jacksonville stop with a rich man (who unbelievably left him only a tiny tip of ten cents). They were bound for southern Florida on his "yat-chet." At the West Palm Beach dock as Hackensacker's yacht moors itself, a dinghy pulls alongside with Hackensacker's oddball heiress sister onboard. She is Princess Centimillia (known as "Maude") (Mary Astor), a breathlessly fast-talking, much-married society woman with wavy, permed hair who calls her brother Snoodles. The Princess is not accompanied by the Prince (he's "all washed up") but by a comic, incomprehensible, European character named Toto (Sig Arno) - an abused, fetch-and-carry foreign suitor ("She goes out with anything," according to John). The effete Toto virtually speaks only four words throughout the film ("Hello," "Yitz" (for yes), "Nitz" (for no), and "Grittinks"), and is possibly a native of Baluchistan: "Toto's a refugee from his creditors, I think."

Maude is amazed that her brother, normally "stiffer than a plank," has attracted such a pretty woman to his company. When she hears that Gerry was nobly rescued, the story is spoilt: "I had hoped for once he hadn't done anything noble. That he was really cooking with gas." She is anxious to find another husband, and tells the soon-to-be divorced Gerry that they can share their man-hungry, predatory passions together: "I don't think I'm quite through with the Prince, either. We can look for new husbands together. I'm thinking of an American at the moment. It seemed more patriotic."

Gerry's errant, forlorn spouse has a bouquet of roses for her on the quay, but he is first spotted by Maude noting him as a "very handsome man...I thought I knew all the handsome men in this village. We could use some new faces." Gerry is horrified to see him and fears that he will identify himself, thereby losing Hackensacker's interest and the ruination of her plans ("...I'm doing this for you too"). Gerry forces her husband to go along with her deceptive pretense that she had asked for earlier - he is identified as her brother with the odd name of Captain McGlue. [Gerry is now confronted with difficult circumstances - a choice between a rich man and his vast wealth, and her poor, dreamer husband.] The Princess immediately falls for Tom (Gerry claims he's not married but "entirely free") and invites both of them to stay at her mansion. Toto is assigned the task of carrying Gerry's packages from the Jacksonville store purchases - to keep his hands full so that she can take Tom's arm:

Princess: Toto, this is Captain McGlue. I'm going to see more of him and less of you from now on...Listen carefully, dear, I left my handkerchief...on the yacht. You go fetch it. Si?
Toto: Nitz.
Princess: Yitz, Toto.
Toto: Nitz.
Princess: (rudely) It'll be 'Nitz' to you, Toto.

She leads him away, privately admiring her new American prey: "How wonderful it is meeting a silent American again...All my husbands were foreigners and such chatterboxes. I could hardly get a word in edgeway." According to John, the Princess can exercise a tenacious, ravenous hold on men that she is attracted to: "My sister and your brother. It would be nice if something came of it...Of course, she's no bargain, but it might happen very easily. She's a woman of iron determination and once her mind is made up, you might as well yield." In her art deco mansion, Maude is much more worldly, risk-taking and overtly sexual (almost nymphomaniacal) than her circumspect, marriage-revering brother. She would marry "Captain McGlue" the next day if she could even if it led to a rapid divorce, musing: "Nothing is permanent in this world except Roosevelt, dear." She encourages her sibling's amorous behavior, but he admits he must wait until the attractive Gerry is divorced and "free." Maude is horrified that her brother considers borrowing some children and having a pre-marital "mock marriage" to test Gerry's maternal instincts.

Once they are settled, Tom blasts Gerry's charade and her spur-of-the-moment, unintentionally-insulting name for him: "But why Captain McGlue? Of all the idiotic names...What am I supposed to be Captain of, a garbage scow?" She explains her self-sacrificial, romantic interest in Hackensacker as a way to get money for Tom to build his beloved dream - an airport. A Staffordshire, porcelain statue of two romantic "lovebirds" is placed on the mantlepiece to indicate, symbolically, whether either of them has been unfaithful and has engaged in an impropriety (had sex) with their partner: "So long as that's there, you won't have the slightest, smallest thing to be unhappy about. That'll be a signal, and we'll never have to mention the subject. And that goes for you, too...and your friend the Princess you seem to be cutting such a groove with."

When Hackensacker and her husband bicker together, Gerry is caught in the middle: "I feel like a bone between two dogs." An effeminate Toto arrives, ready to play tennis with shorts, a racket and mesh bag of balls, and a bill-shapped cap. Maude is flabbergasted, and laughs fitfully about her brother's old-fashioned, mock courtship of Gerry: "It's too, too excruciating...He wants a miniature marriage with you...you know, everything up to the dissolve, and then goodnight sweetheart, I'll see you in the morning...The boy wants to bundle!...And then he's gonna make you cook and sew and wash the windows. And then he's gonna get some little brats to see if you know how to change their (diapers)...He's going to rent them." Hackensacker gets on bended knee to confess and declare his affections to Gerry: "However ridiculous I may seem, there's nothing ridiculous about the way I feel in my heart. I'm madly in love with you."

At a dinner-dance at the Everglades Club, the sexually-hungry Princess, dressed in a glittering gown, dances with a tuxedoed Tom on a dance floor surrounded by palm trees. She remarks that he should grab her tighter instead of letting her flop around: "You will care for me, though. I grow on people - like moss." While Gerry dances with Hackensacker, she finds the opportunity to tell her billionaire suitor that her brother has a scheme to build a suspended airport "stretched like a tennis racket." Hackensacker promises to help finance it with a hundred thousand dollars. Meanwhile - as the scene cuts back and forth between the two couples, the Princess informs an astonished Tom about her brother's plan to buy off Gerry's husband for $99,000 so that she'll be able to obtain a divorce. When seated after the dance, Gerry tells her brother the good news - "Snoodles is going to build your airport for you." In love with Gerry, Hackensacker also gallantly vows to pay off her husband (a "human bacterium") since it's "cheaper to pay than to fight."

Being principled, morally honest and practical - and hateful toward Hackensacker for courting his wife, Tom adds to the complications of the plot by trying to sidetrack Gerry's scheme, as he always does. He thanks Hackensacker for monetary support to help him build a model of the airport. But then he confesses how he is involved from two fronts - both as Gerry's inventor/"brother" and as the partner of Gerry's husband - who has already been labeled a "skunk" and a human bacterium: "I'm awfully sorry to hear that about Tom. I knew he was a failure and a dreamer, I guess, but I didn't know he was a skunk. It's very kind of you to want to build the airport - I mean the model of it. I guess I was a little too stunned to say 'thank you,' but you know how it is when you've been waiting for something for a long time. There's only one trouble with the whole set-up, something that Gerry neglected to tell you. And that is that I'm not alone in this invention. That human bacterium we were talking about, her husband, has had exactly as much to do with it as I have. So you see, if you help me, you'd be helping him too. I know that nothing could be further from your wish."

Later after taking him away onto the dance floor, Gerry scolds her husband as a "fathead" for being stubbornly "noble," causing an impediment, refusing the rich man's patronage ("twice already"), and ruining his American success story. Worried that her powers are being undermined, she fears that Hackensacker may consider backing off from his idea of underwriting the airport altogether. Tom pleads that his destiny is already fatalistically determined ("the way you are is the way you have to be"):

Gerry: Can't you ever learn to be practical? Don't you know that the greatest men in the world have told lies and let things be misunderstood if it was useful to them? Didn't you ever hear of a campaign promise?
Tom: The way you are is the way you have to be, honey. That's the way I am and if I'm supposed to be a flop...
Gerry: You're not going to be a flop. Nobody's who's been married to me for five years is going to be a flop. You're going to get your airport if I have to build it for you myself - after I'm married.
Tom: After you're married. It's a funny thing to hear your wife say.

Hackensacker resolves the dilemma by deciding to placate Gerry's "scoundrel" husband and invest in the airport: "I've got it. I'll build it and his share will be more than $99,000 dollars so he'll have to release you." Toto watches from a dining table, where he plays cards by himself - with a miniature deck. When they drive back to the mansion, he pops out of Tom and Maude's backseat, and then takes a pratfall - he painfully somersaults headfirst out of the car, after Maude has berated him: "I suppose he'll show up, he always does...Wouldn't he be awful to be married to? Always hanging around." At the top of the stairs - with "Topic A" on her mind, a sexually-pre-occupied Maude pours out her voracious heat on Tom. When Tom later overhears Hackensacker's clucking delight over Gerry and their future together ("Now, with you and Mac and the airport, I can see great days ahead full of fun and everything") and warns her of a "surprise" he has planned for her in a few minutes (he suggests that she leave her balcony window open), Tom, already sexually frustrated, smashes the porcelain figurine behind his door.

She scolds Tom after noticing the statuette's pieces on the floor: "So you couldn't even wait a decent interval, you and your Princess! I hope you're very proud of yourself, Captain McGlue." He explains that it was handy and didn't signify anything further, and then vows love for her: "...you can't blame a man for trying to hold onto something that he loves, that he always has loved, and always will love..." She steadfastly struggles to resist changing her mind about her plan to divorce him, have Hackensacker as a husband, and to fix up her "brother" as a successful inventor with a fully-paid up airport: "You're gonna make me cry...No, you're forgetting the airport, you're forgetting everything that counts...No, it's all finished. When you make a decision, you have to stand by it, and you can't let champagne or tree toads, or nightflowers, or memories get in the way of it. It's all over and I know it's for the best...Oh no, now listen to me just this once, will you? I've always done what you wanted and it's always turned out a disaster. Goodnight darling, sleep tight." However, at her bedroom door (with an intervening sitting room in between), she succumbs and gives her jealous "brother" a goodnight kiss - the first step in the restoration of their romance.

In one of the best scenes of the film, Hackensacker has rented a full orchestra and he unwittingly serenades Gerry with Good Night, Sweetheart below her balcony in the garden. Upstairs, Gerry struggles to unzip the back of her strapless dress. She hesitantly moves through the sitting room to requisition assistance from Tom next door ("I can't open this blasted dress") - this is the second time she surrenders to him in the film. Gerry sits on his knees as he fiddles with the fastener to help remove her dress - the serenade puts her into a weakened, romantic mood and she collapses in his arms: "Oh, darling, darling, darling." As the song ends, Tom is amorously affectionate with Gerry and seduces her within his own bedroom, as she ruefully remarks: "I hope you realize this is costing us millions."

The morning after, Toto is dressed in polo togs and enters the Princess' bedroom while she is dining on breakfast in bed. She again caustically berates him and tries to permanently dispose of him: "I suppose it takes an iron constitution to be a houseguest...Why don't you go away someplace? There must be somebody else who can use a houseguest. I can't be the only sucker in the world. Why don't you go to Havana? That's a nice place and I'd treat you to a nice one-way ticket." John excitely enters the bedroom in a hurry to propose to Gerry, with a huge jeweled ring (a "chip" from the "Hope Blue") in a jeweller's box he has just purchased at Margetsons. The Princess surmises that his intentions will be obvious: "I think she'll know what you mean." She opens another box displaying a shiny pocket watch, chain, and penknife - her gifts for Captain McGlue.

When Hackensacker sees both Gerry and Tom packing, Gerry returns her bracelet and renounces him - and all his wealth! - over her own husband. She turns down the great temptation of wealth, and takes back her husband, explaining: "I let you think much worse about him than he is." But she allows herself one quick look in the jewelry box, and then pushes it away: "There's a limit to what a woman can stand." Hackensacker is broken-hearted, disappointed and depressed by Gerry's decision: "I'll never get over it as long as I live. I had such hopes and such plans." But he still mentions keeping his promise as a benefactor to finance McGlue's airport: "Anyway, we still have the airport. That will keep us busy."

When the Princess arrives ("What's knittin' kittens?"), Gerry confesses the real nature of her masquerade to the surprised, but understanding pair:

Gerry: He isn't exactly my brother...He's my husband!
Princess and John: (together) He's your husband!
Tom: That's right.
Princess: Well, no wonder. I thought I was losing my grip!
John: You mean the vermin who, who, who...(To Gerry) That's right, you said he didn't.
Princess: Then who is McGlue?
Tom: There is no McGlue.
Princess: Well, thank heavens for something. That name!

Hackensacker reaffirms his financial backing of the Jeffers airport "on a purely business basis," reasoning that "if an idea has merit, it has merit. Sentiment and business don't belong in the same bed." The neat, rapid denouement of the film is provided by a lucky coincidence (or weak plot contrivance) - both Tom and Gerry are identical twins. Their sister and brother provide an heir for John and a husband for the Princess:

John: (joking) I don't suppose you have a sister?
Gerry: Only a twin sister.
John: A twin sister!
Gerry: Oh, didn't you know about that? That's how we were married in the beginning - both being twins.
Tom: Of course that's another plot entirely.
Princess and John: (in unison) Both twins! (To Tom) Are you a twin? (Tom nods.) (To Gerry) Are you a twin? (Gerry responds, "Yes.") Well, what's he/she doing?
Tom and Gerry: (together) Well, nothing, you see.

The film returns to the same altar of the wedding chapel during the title sequence, to the tune of the Wedding March. There, in a final wedding tableau using trick photography, the camera pulls back to reveal three couples all united in a triple ceremony by marriage (from left to right) - wealth is wed into both Tom and Gerry's families:

• Tom and Gerry (as Best Man and Bridesmaid)
• Hackensacker and Gerry's twin (in a wedding gown)
• Tom's twin and the Princess (in a wedding gown)
• Toto

Now, both twins from the opening have found their own mates - although with some trepidation. The camera again tracks back to the same framed titles to provide a cynical footnote:

and they lived happily after - or did they?