Appearing foolish to his father and everyone else, due to his confused neuroticism over Jean/Eve's identity, Charles also isn't watching where he's going as he is distracted by Muggsy motioning from outside at Eve. In the first of a couple of magnificent pratfalls, he trips and dives right over a low sofa couch (that's been there for fifteen years), ending up on top of a coffee table with his head in a bowl of lobster dip. The guests turn in astonishment when they hear the loud clatter of glasses and appetizers. As she defends his awkwardness, Eve delicately peels appetizer sandwiches off the front of his black tuxedo. She suggests that Charles go upstairs and take a bath to clean up and then promises: "I'll like you just as much as ever. There's a good boy." As he starts for the stairs and she continues to proceed to the dining room, he waves at her with moon-eyes, neglecting to again look toward where he is going. Compounding the catastrophe, he falls into the hanging portieres (drapes), gripping and taking them down with him as he crashes to the floor. He sheepishly smiles up at her.

As Charles puts on a clean white tuxedo in his room after cleaning up, Muggsy is reasonably convinced that Eve is Jean: "That's the same dame. She looks the same, she walks the same, and she's tossing you just like she done the last time." He argues that masquerading as someone else is easy - he does a Hitler impersonation to prove his point. Charles refuses to believe that Jean Harrington and Eve are one and the same person: "They look too much alike to be the same." Charles explains why he is persuaded that she is not Jean - it is because she has made no attempt to disguise or change her appearance by dyeing the color of her hair or changing her eyebrows:

If she came here with her hair dyed yellow and eyebrows different or something...But she didn't dye her hair and she didn't pretend she'd never seen me before which is the first thing that anybody'd do. She says I look familiar...If she didn't look so exactly like the other girl, I might be suspicious, but you don't understand psychology. If you wanted to pretend you were somebody else, you'd glue a muff on your chin and the dog wouldn't even bark at ya.

When Charles joins the guests at the dinner table, Muggsy intercepts the serving platter of roast beef, so he can sneak over and advise Charles one more time. As the serving platter is taken from him by the head waiter above Charles, it twists away from Muggsy's hands and the beef roast and gravy rolls onto Charles' suit. He rises, dripping with food, as his father snidely comments: "Why don't you put on a bathing suit?" After changing again, this time into a white dinner jacket, Charles has missed dinner and joins everyone in the living room. He is worried that has been humiliated and that Sir Alfred's niece will disapprove of him as a half-wit.

Then to avoid further suspicion from Charles, Sir Alfred invents a secret tale of two daughters (a good one and a bad one) in the Sidwich family, a tale ("the skeleton in our family closet") unknown to Lady Eve: "I'm afraid you've stumbled on the sorrow of Sidwich, the secret of the century." Lady Eve's elderly father, the Earl, married Eve's younger mother in a "May-November romance, even a March-December." As Sir Alfred surreptitiously relates the shameful story, he tells Charles: "Into the gulf that separated the unfortunate couple, there was a coachman on the estate, a gay dog, a great hand with the horses and the ladies, need I say more...They called him 'Handsome Harry.'" Charles recognizes Colonel Harrington as the 'Handsome Harry' character: "That's the father of the girl on the boat." According to Sir Alfred's scandalous story, the two daughters look like identical twins:

Sir Alfred: Of course it is, the father of the other child, after the divorce, of course.
Charles: But they looked exactly alike.
Sir Alfred: We must close our minds to that fact as it brings up the dreadful and thoroughly unfounded suspicion that we must carry to our tombs, as it is utterly untenable that the coachman, in both instances...need I say more?

Charles buys the ruse and vows to keep the secret intact ("silence to the grave and even beyond") that Lady Eve is the half-sister of a black-sheep twin, Jean Harrington. As Charles crosses the room to talk to Lady Eve, he helps her uncatch her train from under a chair leg. As he rises from his squatted position, he upends a tray of coffee service above him. The contents of the tray are tipped over onto him - covering him with black coffee.

After the party, at Sir Alfred's breakfast table, Eve explains why they both she and Charles had difficulty recognizing each other, and Sir Alfred tells about his devious story. She divulges her plan to ensnare Charles and make him fall even further:

Sir Alfred: I took the further precaution of telling him the plot of Cecilia, or the Coachman's Daughter, a gaslight melodrama...I filled him full of handsome coachmen, elderly Earls, young wives, and the two little girls who looked exactly alike.
Eve: You mean he actually swallowed that?
Sir Alfred: Like a wolf. Well, and now that you've got him, what are you gonna do with him?
Eve: I'm going to finish what I started, I'm going to dine with him, dance with him, swim with him, laugh at his jokes, canoodle with him and then one day, about six weeks from now...(A manservant enters with an enormous box of long-stemmed red roses from Mr. Charles Pike.) It won't even take six weeks. One day, about two weeks from now, we'll be riding in the hills, past waterfalls and mountain greenery, up and down ravines and around through vine-covered trails, 'til we come to a spot where the scenery will be so gorgeous, it will rise up and smite me on the head like a hammer. And the sunset will be so beautiful I'll have to get off my horse to admire it, and as I stand there against the glory of Mother Nature, my horse will steal up behind me and nuzzle my hair, AND SO WILL CHARLES, THE HEEL.

As she describes her plan and conjures it up, the scene shows the two of them riding through some trees while the sun sets magnificently. In a humorous proposal scene, they stop their horses to admire the sunset and then dismount. He amorously nuzzles up next to her - between her and her horse, and she sharply shouts: "Stop that!" but then realizes it's him and not the horse. Charles falls in love with her all over again and tells her what he is thinking about, as she stands smiling and transfixed while gazing at the sunset. While he proposes to her [the second of two very similar love speeches delivered by him to his fantasy love interest], one of the horses keeps getting in his way:

Charles: I think that if there's one time in your life to be careful, to weigh every pro and con, that this is the time.
Eve: Oh yes, you, you can't be too careful.
Charles: That's right. Now, you might think that having known you such a short time...(The horse nuzzles against his head)
Eve: I-I feel I've known you always.
Charles: That's the way I feel about you. (The restless horse behind them whinnies and butts between them with its nose.) I don't just see you here in front of the sunset. But you seem to go way back. I see you here but at the same time, further away and still further away, and way, way back in a, a long place like a...(The horse nuzzles against him again.)
Eve: Like a forest glade.
Charles: That's right. How did you guess?
Eve: Because, that's where I see you always. We held hands, way, way back.
Charles: Why, that's remarkable. That's like telepathy.
Eve: I can read many of your thoughts. (The camera angle abruptly shifts, taking their perspective from behind as they look at the sunset.)
Charles: Then, I need hardly tell you of the doubts I've had before I brought myself to speak like this. (He pushes the horse away one more time.) You see Eve, you're so beautiful, you're so fine, you're so...I don't deserve you. (The camera returns to the original, head-on shot.)
Eve: Oh but you do, Charles. If anybody ever deserved me, you do. So richly.
Charles: Eve!
Eve: Charles! (The horse whinnies as they embrace.)

Her plan works - but she threatens to expose Sir Alfred by 'hooking' Charles a second time. He threatens to telephone her father that she has accepted Charles' marriage proposal (with plans to dump him). The film presents a short, wordless montage sequence leading up to the wedding and the ceremony itself. On the stairs of the Pike mansion, Charles hugs his mother and tells his father of the news. Sir Alfred notifies Col. Harrington by phone. A cake (that increases in layers) is decorated in the kitchen of the Pike mansion. The Pikes and Muggsy are fitted into their wedding attire. Finally, Eve descends the Pike stairway in her satiny wedding dress with a long flowing bridal train. The wedding march thunders out as she appears on the arm of Sir Alfred and comes into the Pike living room, arranged for the stylish wedding. As Charles joins her at the altar, she turns and gives him a peculiar smile.

Gerald and Colonel Harrington, who have not attended the wedding, discuss the scorned Eve's motives for marrying Charles and wonder how she will reap her revenge and "teach him a lesson" on their honeymoon train:

Harrington: ...now she's honeymooning on a train with a man she hates.
Gerald: Maybe she's gonna shoot him.
Harrington: She's afraid of guns.
Gerald: Maybe she's gonna push him out of the window.
Harrington: No. You can't open a window on a train.

On a speeding train headed for their honeymoon, in the film's funniest sequence, the screwball comedy couple are fatefully brought together again. The train barrels forward in the night - and toward the camera. In the train's interior, Charles - in his bathrobe and pajamas - gets a drink of water, and then knocks on the door of their "cozy" compartment. Inside is Eve, dressed in her sheer negligee and looking at him as he enters. A piece of luggage tumbles onto his head from above, and she comforts and pets his head as they sit on their bed. She suddenly starts laughing hysterically, recalling "that other time" when she eloped at the age of sixteen and traveled third class with a young stable boy named Angus - but the boy was "no one of the slightest importance." After she's "planted a seed" in his curious, determined-to-know mind, she reluctantly tells him more details, as Charles' eyes bug out and he chokes with disbelief. It took her parents weeks to locate them and when they were brought back, the boy was "discharged." Charles hopes that they were brought back before nightfall. On the contrary, explains Eve: "It took them weeks to find us. You see, we'd make up different names at the different inns we stayed at."

Her preposterous story is interrupted by lightning strikes and flashes and exterior shots of the train as it roars through a thunderstorm, signifying how upset and overwhelmed Charles feels. He paces silently and contemplatively in their compartment. He stops and sits on the bed after deciding to swallow his pride and maintain his composure. In noble fashion but with clenched teeth, he forgives her (with "understanding and sweet forgiveness") for her past youthful indiscretions [to the tune of the Pilgrims' Chorus on the soundtrack]:

I won't conceal from you that I wish this hadn't happened but it has...and so it has. A girl of sixteen is practically an idiot anyway, so I can't very well blame you for something that was practically done by somebody else. I want to thank you for being so frank. The name of Angus will never cross my lips again and I hope that you will do likewise. Now, let us smile and be as we were.

She is pleased by his decision, puts her arm around him, and supportively says: "I knew you'd be that way. I knew it the first moment I saw you standing beside me - I knew you'd be both husband and father to me, I knew I could trust and confide in you. I suppose that's why I fell in love with you."

Eve resumes telling an amorous Hopsie about other previous partners, leaving no stone unturned to cause him to become disillusioned with her. She decides to reveal more of the increasingly sordid, lurid details of her nymphomaniacal past as she flaunts her promiscuousness. She casually assaults and psychologically punishes him again with another tale about Herman: "I wonder if now would be the time to tell you about - Herman?" Charles gasps. Her words are drowned out by another exterior shot - the timely roar of the train entering a tunnel [an obvious sexual cliche], torrential rains, train whistles, and a sign reading: "PULL IN YOUR HEAD - We're Coming to a TUNNEL."

Further sequences are displayed through montages, switching back and forth between exterior and interior shots, with the revelation of other names from her insatiable past including Vernon ("Vernon was Herman's friend"). She cleverly and convincingly reveals previous elopements and amours. The train whistles and roars after Charles' reaction: "What a friend!" And then there was Cecil: "It's pronounced Ce-cil." The train's whistle sounds again, and they continue to battle together under the roar of the engine. Even more partners include Hubert and Herbert ("They were John's twin cousins") - and John.

Utterly dazed, disgusted, and disillusioned by all her experiences and driven jealously mad, pajama-clad Charles (with an overcoat and hat) gets off the train as it slows at the next stop. He hastily escapes from their nuptial room, tosses his suitcases from the train and stumbles off, slipping and slowly falling down in the mud - another ignominious, humiliating fall onto his back. One leg is left extended up into the air. Eve's plan succeeds and she is vindicated, but as she sits victoriously at the train window to watch Charles and draw down the shade, she is neither laughing or triumphant, but inexplicably forlorn, defeated and ruined herself.

Now Eve has a perfect opportunity to seek a large settlement from Pike's lawyers, in exchange for giving Charles a divorce, financial gain that excites Colonel Harrington - similar to a 'royal flush': "For once that we have a chance to make some honest money..." Eve/Jean replies: "Oh, tell 'em to go peel an eel." But she realizes, once again, with a change of heart that she has hurt her chances with Charles and that she still loves him and wants to take him back. When Charles' father phones her about the settlement from his office (surrounded by a large contingent of advisors in front of a Pike's Ale sign), she nobly proposes going through with the divorce free of charge without alimony. However, she asks for only one thing - for Charles to come, in person, and speak with her in New York when he seeks a divorce: "I want to see him first and I want him to ask me to be free. That's all. No money, no nothing....there's something I want to say to him before we part." She is told that Charles refuses to talk to her after their honeymoon experience. He is unavailable anyway to dissolve their marriage - he's gone to say goodbye to his mother. He is scheduled to leave town, sailing that evening on the S. S. Southern Queen from Manhattan. So Lady Eve and Charles remain bound to each other in a marriage of miserable despair.

The film's final scene seques into another shipboard meeting, where Charles is seen roaming the ship in a trance. Reverting to her former self as Jean Harrington, she takes the same steamship, and once again 'accidentally' trips him as he walks through the smoking room just as she did earlier when they first met. He rediscovers his cardsharp playing companions - this time, he is ecstatic about being reunited with both Jean and her father. He ardently embraces and passionately kisses her. He orders champagne for the Colonel, but is determined not to let Jean go this time. They hurry from the smoking room toward her deck and cabin stateroom. He drags her down many flights of staircases toward her room where they will presumably consummate their passions. Both are regretful and realize they have learned something about love.

They are reunited in a happy, romantic ending to their farcical affair involving conflict, deceitfulness, and confusion. Giving up her malicious heartlessness and manipulative cunning, Jean has succumbed to love and her Prince Charming. After rejecting Jean/Lady Eve twice on the grounds of immorality, a lovesick and innocent Hopsie thinks he has luckily met Jean Harrington again rather than Lady Eve Sidwich - he momentarily tries to protest that he shouldn't be in her cabin with her since he is married:

Jean: You really haven't the right to drag me off like this, Hopsie...Why didn't you take me in your arms that day...Why did you let me go? Why did we have to go through all this nonsense? Don't you know you're the only man I ever loved? Don't you know I couldn't look at another man if I wanted to? And don't you know I waited all my life for you, you big mug.
Charles: Will you forgive me?
Jean: For what? Oh you mean, on the boat. The question is, can you forgive me?
Charles (naively): What for?
Jean: Oh, you still don't understand.
Charles: I don't want to understand. I don't want to know. Whatever it is, keep it to yourself. All I know is I adore you. I'll never leave you again. We'll work it out somehow. There's just one thing. I feel it's only fair to tell you. It would never have happened except she looked so exactly like you. And I have no right to be in your cabin.
Jean: Why?
Charles: Because I'm married.
Jean (softly): But so am I, darling. So am I.

After the classic closing line, she pushes her cabin door shut and he stays in the room with her - they are a legally married couple! [From Hopsie's vantage point, he is willing to surrender to her and commit adultery because of his overwhelming, unconditional love for her.]

In the film's final fadeout, after a few seconds, Muggsy stealthily sneaks out of the door of their stateroom and closes the door behind him. He looks straight deadpan into the camera and delivers the final line of dialogue in the film. He refers to Jean's dual identity as a crook and as a phony - and to the archetypal Eve whose rebellious behavior led to the Fall of Man in the Garden of Eden:

Positively the same dame!

The animated snake returns during the final close-out, weakly shaking a mariachi and offering a contented, tired smile. The beguiling serpent curls around two snuggling apples ("THE" and "END") from the tree of knowledge of good and evil in the Garden. The snake is pleased to have brought together two essentially frail, emotionally incomplete human beings who need each other to fill the voids in their lives.