In the next scene, Lucy tells Aunt Patsy that she is beginning to be convinced that Jerry wants her back - otherwise he wouldn't make such a fool of himself for her sake: "Jerry's always had the most fantastic way of getting into scrapes. Oh, we've had some grand laughs together." She confides that she is breaking off with Leeson:

I can't marry him because I'm still in love with that crazy lunatic and there's nothing I can do about it...I tried to forget Jerry.

Her French singing teacher (invited by Lucy) arrives - and after placing his derby hat by the front door - is told her resolute decision: "I'm convinced he must care about me or he wouldn't do the funny things he does." She schemes with him for a favor - to persuade Jerry of her original innocence: "I wondered if you could convince him that everything was just as I said it was that night at the inn. You know the night....And by all means, he mustn't know that I had anything to do with it." When Jerry drops by - with his own brand-new derby hat - Lucy shoves her gentleman caller Armand into her bedroom to hide him.

In the funny episode [later termed the "two men in a bedroom farce"] regarding the dual derby hats and a clever dog, Jerry has unexpectedly come to apologize for his "behavior" at Duvalle's studio/apartment: "I certainly acted like a prized lunatic and I'm sorry...Nothing except the most ridiculous and sickening exhibition mortal man ever made of himself. Oh, I don't know why I act like that....The main idea is, do you accept my apology? Aside from making a blue-ribbon sap of myself today, I must have embarrassed you beyond words. You took it fine, though." During their conversation, Mr. Smith has persistently retrieved and brought out, in a game of hide and seek, Duvalle's incriminating derby hat from behind a flower arrangement and a mirror where Lucy has stashed it. Lucy struggles to conceal its whereabouts behind the couch, but fails when Mr. Smith fetches it from behind the mirror. When Jerry puts what he thinks is his derby on his head, the over-sized, "roomy" hat descends down over his ears. Quizzically, he looks at himself in another mirror: "Well that's funny, I only bought the hat an hour ago and look at it."

From across the hall, Daniel and his "Maw" show up for a chat, so Jerry is forced to duck into Lucy's bedroom where Armand is hiding: "He'd better not find me here. I'll duck in the other room." Behind closed doors and off-screen, the two have a noisy fist fight - to everyone's astonishment: "What on earth was that?" Lucy listens helplessly as the crashing from her bedroom intensifies, as Mrs. Leeson speaks glowingly of Lucy and vows her innocence. The two brawlers rush through the living room and out the door into the hallway, with Jerry chasing Armand. This compels Aunt Patsy to declare: "They forgot to touch second." That's enough evidence for an astonished Mrs. Leeson and her dumbfounded son: "Come on, Dan." Daniel remarks: "Well, I guess a man's best friend is his mother. I certainly learned about women from you."

In the newspaper, Lucy reads about Jerry's romance to a "madcap heiress," New York socialite Barbara Vance (Molly Lamont): "Millions of dollars and no sense." The caption below the picture reads: "Miss Barbara Vance, debutante and heiress, with Jerry Warriner, vacationing at Bar Harbor and apparently enjoying each other's company. In a montage, Jerry and Barbara enjoy horse polo, boat racing, horse races, a football game, and a casino nightclub. The society gossip columns report their impending engagement: "The Jerry Warriner-Barbara Vance romance reaches the engagement stage as soon as the Warriner divorce decree becomes final, which incidentally, is today."

On the final day of their marriage (their divorce becomes final at midnight), Lucy visits Jerry at his apartment to ostensibly wish him luck - and to win him back. He expects a successful future with his fiancee: "I think Barbara and I will be very happy together." They share a glass of chilled wine and Lucy makes an ambivalent toast: "Let's drink to our future. Here's hoping you and Barbara will be very happy - which I doubt very much...as we go down life's highway, you going your way [with a weaving hand gesture] and I going my way [with a straight path hand gesture]." Lucy encourages sentimental memories of their own initial romance as they open a bottle of champagne - with weeping violins in the background:

I think champagne is so fitting to round out our romance. I remember the first drink we ever had together. You in your very best manner said, 'It must be champagne.' And then you offered a toast, you remember?...Being a woman, I do... You said, 'Lend an ear I implore you. This comes from my heart. I'll always adore you. Til death do us part.' Remember?...Oh dear, well, it was pretty swell, I mean, while it lasted, but uh, all beautiful things must end, so, I guess we may as well call it a day.

Jerry keeps a firm, stiff upper-lip without succumbing to sentimentality during their farewell drink.

When the phone rings and Lucy answers it, Jerry stalls while trying to think of an alibi for having a woman in his apartment. When he returns to the phone, Barbara asks: "Have you made up your mind who the woman is?" After consultation with Lucy, Jerry pretends that she is his sister who "just got back from Paris, bopped into see me, you know." Barbara invites his "sister" to join them for their evening dinner party at the home of her stuffy, upper-class, parents - Mr. Vance (Robert Warwick) and Mrs. Vance (Mary Forbes). But the spunky Lucy is resistant about meeting his new, highly-social fiancee: "Tell her I'd love to meet her. Tell her to wear boxing gloves." Meanwhile, Lucy hatches a plan to break his engagement at the dinner party while posing as his imaginary, low-class, ill-bred sister.

That evening at the Vance's palatial mansion - in their library, Jerry explains his 'sister's' absence: "She didn't weather the boat trip very well." He repeats his platitudes about marriage to a slightly-suspicious Barbara:

You can't have a happy married life if you're always suspicious. No. There can't be any doubts in marriage. Marriage is based on faith and if you've lost that, you've lost everything.

Because of everyone's interest in his sister, Jerry describes her to Barbara: "You'd like my sister. She's very much your type...(She went to school) in Switzerland..." He also begins a joke about his father ("a Princeton man...Class of '92"):

He tells some very funny stories about the place in those days too. He tells one in particular about a football game. It seems that Yale was playing Princeton one day and, uh, with the ball on Princeton's two-yard line, Yale fumbled. A minute to go, Dad picked up the ball and ran...

An off-screen door slams as Lucy invades the scene and crashes the high-class dinner party, pretending to be his heavy-drinking, flamboyant and vulgar Southern sister "Lola." The butler (Leonard Carey) formally announces her as "Miss Lola Warriner." She is wearing a flouncy dress with flared-out ribbons on each shoulder, a double-tiered hula-skirt fringe - all decorated with elbow-length gloves. When she is introduced to Barbara, she greets her with: "I've seen your pictures in the paper and I've wondered what you look like." The prodigal sister's first comment to cigar-smoking Mr. Vance is insulting: "I never would have known you from his description." On the couch, she repeatedly accosts Mrs. Vance with her long silk handkerchief.

Lola: (in an apologetic tone, while pulling on her handkerchief) Will you excuse me, Mrs. Vance? Thank you. (Mrs. Vance rises, but Lola is the one sitting on the handkerchief) (Lola delightedly rises and exclaims) Oh look, it's me, isn't it?! (They both resume their seats and Lola again pulls on the handkerchief.) It's you this time, Mrs. Vance. (Mrs. Vance rises again.) Look, I'll just put it over here and get it out of the way. (Mrs. Vance sits down again and shoots upward, after sitting on Lola's hand.)...I guess that could go on and on and on and on.
Mrs. Vance: I hope not!

Hinting at her heavy drinking and alcoholism, she asks for a drink: "Well, I don't want to be rude but may I have a drink?...I had three or four before I got here, but they're beginning to wear off, and you know how that is." She also gleefully insinuates that her 'brother' has a drinking problem to deliberately humiliate him:

We call him Jerry the Nipper. He likes to sneak 'em when nobody's looking. So cute about it too. I've seen him go along a whole evening and apparently not have a thing to drink and all of a sudden fall flat on his puss.

'Lola' has a glass of sherry ordered for her, but whispers a different request to the butler: "Make that ginger ale, please." She gestures for a tall glass. She squeezes herself onto the sofa next to Jerry and Barbara, as Jerry resumes his football joke about his father. She interrupts and revises their entire heritage, making her father the Princetonian landscaper:

What in the world was Dad ever doing with a football?...Of course I remember. Pop loved Princeton. He was there nearly twenty years. If ever a man loved a place, he did - he just adored it. And he certainly kept it looking beautiful. You've seen the grounds, of course?

When the glass of 'sherry' is delivered, she unceremoniously gulps it down, and explains why she was thirsty: "It must have been that ham I had for dinner." Then she sits between Jerry and Barbara, asking: "Mind?" In a gross, chummy fashion, Jerry's crude and gauche 'sister" calls Jerry a "swell' brother ("He's always been pretty swell to me"), and then betrays the fact that she was a dancer at the Virginia Club [the nightclub where Jerry's previous date Dixie Belle Lee worked], until Jerry started dating the wealthy heiress:

I was working my head off at the Virginia Club but the minute he started doing better, you know what I mean, why he made me give up my job and, uhm, take a trip to London and Paris and uh, I think that was pretty swell, don't you?...(at the Virginia Club) it was a little act, kind of uh, well, it's a little hard to explain.

And then she creates a nasty scene when she pretends to lose her purse and looks with steely, accusatory eyes around the room: "Sa-ayy wait a minute! Don't anybody leave this room! I've lost my purse." It has fallen between the cushions on the couch, and she is relieved: "Oh, well, am I relieved!" Speaking from the side of her mouth, she bestows her purse to Jerry for safe-keeping: "Kinda keep an eye on that for me?"

To show them how she dances, she demonstrates with a reverential, simulated rendition of Dixie Belle Lee's vulgar nightclub routine and song, My Dreams Are Gone With the Wind, assuring Jerry: "I'm not going to do it the way I did at the club, if that's what you're afraid of. Think I'm a fool?" Lola describes her family's own antiquated phonograph player when Barbara searches for music to play: "The one we've got at home you just wind." She advises her audience to use their imaginations: "The number has some wind effects in it but you'll just have to use your imagination about them." The appalling performance with side-slapping gyrations, accompanied by a phonograph record, is jazzy and sped-up, and at the moment of the wind machine's blast at the end of each verse, Lola adds: "Woo-woo-woo! Get it?" and buckles her knees. When the song finishes, she exits with a backwards shuffle toward a bemused Jerry at the doorway, who is ready to leave with her. She bows as he escorts her off the stage - and out of the Vance's high-class world.

She tricks him, by pretending that she's drunk, into being driven in her convertible to her Aunt Patsy's mountain cabin. Before they drive off, she turns the volume up full-blast on the car radio set on a jazz station - and throws away the control knob, as he jokes: "That's right, put it where we can find it." A nearby cop orders them to "shut that thing off" and it does when the hood slams down. During the drive, Jerry explains how he intends to only drop her off at the cabin. He argues with Lucy about her orchestrated plan to have him spend an innocent night at a country inn with her:

Jerry: You just thought that if I'd stay up there, you'd show me exactly how innocent a night in the country could be, didn't you?
Lucy: Are you still harping on that same old string? Well, it's a matter of complete indifference to me whether you go or stay. I was just trying to make it easier for you, that's all.

Two uniformed motorcycle cops (Edgar Dearing and Al Bridge) stop them because the radio has begun blaring jazz again. During the chaotic scene, they discuss the radio problem, the car's ownership and Lucy's ownership card and license number - over the sound of the radio. Jerry is forced to walk the traffic line for suspected drinking, as she yells to him: "Go on, honey, truck it!" She intentionally releases the brake and sends her car over an embankment to cause an 'accident', so that the cops have to transport the stranded couple to her Aunt's cabin. She bounces up and down on her bike during the windy ride, causing the police siren to sound.

At the rustic cabin where Lucy has set up their final rendezvous [to get back together and reconcile], she feigns surprise that her Aunt isn't there: "She isn't here?" They retire to adjoining, but separate bedrooms on the last evening of their ninety-day waiting period before their divorce is final at midnight. In her room, she tightens up the silky, sexy, loose-fitting nightgown borrowed from her Aunt Patty's drawer. The door between their rooms has a weakened and faulty latch, and it blows open - exposing Jerry in his oversized night-shirt. She laughs at his "air-conditioned" garment. The door latch "isn't very practical," although Lucy prophetically guesses "it will serve its purpose." The door is seemingly blown open by the power of their mutual attraction.

Jerry surreptitiously finds excuses to keep opening the door, coming and going through it in a cat-and-mouse game. After shutting the door, Jerry reopens it and says goodnight for the second time. A gigantic cuckoo clock above Lucy's door, reading 11:15 pm, has a mechanical, male and female Alpine character (with lederhosen and a mountain maid's dress) that emerge in separate doors to signal the quarter, half hour, and hour. Unable to sleep in their respective beds and longing to be reunited, both lie awake and listen, each hearing the wind rattling the door. At 11:30 pm, the door opens and both are startled to see each other rising and sitting up in bed. Jerry gets up and approaches the door, and they discuss his initial feelings of suspicion - all in his mind:

Jerry: I told you we'd have trouble with this...In a half an hour, we'll no longer be 'Mr. and Mrs.' Funny, isn't it?
Lucy: Yes, it's funny that everything's the way it is on account of the way you feel.
Jerry: Huh?
Lucy: Well, I mean if you didn't feel the way you do, things wouldn't be the way they are, would they? Well, I mean things could be the same if things were different.
Jerry: But things are the way you made them.
Lucy: Oh no. No, things are the way you think I made them. I didn't make them that way at all. Things are just the same as they always were, only you're the same as you were, too, so I guess things will never be the same again. (seductively) Good night.

At eleven forty-five, Jerry opens his cabin window to coax in a gale, but the restless black cat in Lucy's room lies across the door and holds it shut. When Lucy notices the cat blocking the doorway, she shoos it away, finding Jerry kneeling on his hands and knees outside her door and inspecting the problem. She languishes provocatively on her bed as he enters her room and admits to being a suspicious fool:

Lucy: You're all confused, aren't you?
Jerry: Uh-huh. Aren't you?
Lucy: No.
Jerry: Well, you should be, because you're wrong about things being different because they're not the same. Things are different, except in a different way. You're still the same, only I've been a fool. Well, I'm not now. So, as long as I'm different, don't you think that, well, maybe things could be the same again? Only a little different, huh?
Lucy: Do you mean that, Jerry? Are you sure?
Jerry: Hmm, hmm.
Lucy: No more doubts?...No more being...?
Jerry: Except, uh...
Lucy: Except what?
Jerry: Well, there's only one thing that bothers me.
Lucy: What?
Jerry: (The door opens) This darn lock.
Lucy: Oh, is that all?

She has gestured at a chair in her room, and he wedges the door shut with it - on her side of the room. After locking himself in his wife's room, she settles back on the bed and laughs at her perplexed husband, as the clock strikes midnight. They learn "the awful truth," decide they are irresistible to each other, and reconcile their differences to make things the same again at the last-second. The divorced couple are reunited minutes before their marriage is legally supposed to end. [Note: The Production Code forbade their final consummation, however, since midnight made them officially divorced.] Their reunion at midnight is thereby enacted by the cuckoo clock's two tiny figures, symbolic stand-ins for Jerry and Lucy, that both enter the same opening (instead of separate entrances) at the film's suggestive, concluding fade-out.