In Alicia's apartment, the camera moves from a closeup of Alex's gift card invitation and flowers to Alicia (the formally printed "Alexander Sebastian" is crossed out and the more informal signature "Alex" is substituted) up to a shot of Devlin reading a magazine (he is really looking at the bouquet with a spiteful appearance). Prescott watches Devlin as Alicia (wearing white fur and a full-length white outfit) enters the living room from her bedroom. She receives instructions from Prescott while Devlin is silent with his back to the camera. Devlin is uncooperative when she gestures for someone to help her latch Prescott's rented jewelry around her neck. [The camera denies us full access to him and conveys the impression that he assents to having her sent away.]:

Now try to memorize the names of all the people you see there tonight. The men I mean. And get their nationalities. That's very important...And I suggest that you, uh, don't ask any questions. Just use your eyes and ears. They're a pretty keen and desperate bunch. Don't underestimate them.

Prescott advises that Devlin and Alicia "keep shy of each other for the next few days." Alicia is delivered in a limousine to the Sebastian mansion. She is first ushered into the library where she awaits a greeting from Mme. Sebastian (Leopoldine Konstantin, appearing in her only American film, in her last screen appearance). Alex's domineering mother is unsure of Alicia from the very beginning and gives her a frosty welcome. She believes that Alicia betrayed her Nazi father by refusing to testify on his behalf:

Mme. Sebastian: You did not testify at your father's trial. We thought that unusual.
Alicia: He didn't want me to. He refused to let his lawyers call me on the stand.
Mme. Sebastian: I wonder why.

Before Alicia can answer, Sebastian enters the room and 'rescues' her from his mother's cross-examination. He takes her to be introduced to five other guests. Each of the formally-dressed Nazi agents approaches and kisses her outstretched hand.

- Eric Mathis (Ivan Triesault)
- William Rossner (Peter von Zerneck)
- Emil Hupka (Eberhard Krumschmidt)
- Mr. Knerr (Frederick Ledebur)
- and Dr. Anderson (Reinhold Schunzel), a scientist and the guest of honor

In the formal dining room before dinner, Alicia notices that Emil agitatedly points with alarm to one of apparently innocent wine bottles - and then is quickly hushed and calmed down by Alex. The scene ends on a close-up of the wine bottle. After the uneventful dinner party, Emil paces outside closed conference doors. Inside, the men discuss his blunder in pointing out the wine bottle. Although an "understandable slip," it was "a very dangerous slip," and "not the first one - there have been several other lapses before." Together, they plot his elimination and murder.

In their boxes at the racetrack, Sebastian and his mother sit in the front section by the railing, with Alicia's empty seat between them. Mother-controlled Alex complains to his mother when she justifiably finds herself questioning her son's new attraction - he proposes that his mother occasionally smile at Alicia:

Mme. Sebastian: Miss Huberman has been gone a long time.
Alex: Mother, is it necessary for you to always address Alicia as Miss Huberman? I do wish you'd be a little more cordial to her.
Mme. Sebastian: Really, I thought I was behaving very well. Has she been complaining about me? (No answer.) I'm grateful.
Alex: You might smile at her.
Mme. Sebastian: Wouldn't it be a little bit too much if we both grinned at her like idiots?
Alex: Please mother. I want to enjoy myself.
Mme. Sebastian: Is it so boring to sit with me alone?
Alex: Not at all, not at all.

In the racetrack crowd, Devlin finds Alicia (he has previously arranged to see her) and speaks to her in whispered tones. She gives him the names of Alex's dinner guests and describes the incident with the wine bottle with Emil - and the fact that she hasn't seen Emil since. Then, she admits to Devlin "for the record" that she has conquered Alexander by using her experienced sexuality to convince him of her trustworthiness. Uncomfortable with her revelations, Devlin turns icy, punishing and sarcastic. He is not willing to painfully admit that he cruelly and passively let her go to engage in the dangerous espionage plot. Now more infuriated and jealous of her association with Sebastian, and experiencing intensely-wounded pride, he spitefully denies ever having loved her in a lethal torrent of bickering words:

Alicia: You can add Sebastian's name to my list of playmates.
Devlin (stunned and amazed, almost bitter): Pretty fast work.
Alicia: That's what you wanted, wasn't it?
Devlin: Skip it!..I've been recalling some of your remarks about being a new woman. Daisies and buttercups, wasn't it?
Alicia: You idiot. What are you sore about? You knew very well what I was doing.
Devlin: Did I?
Alicia: You could have stopped me. Just one word. But no, you wouldn't. You threw me at him.
Devlin: I threw you at nobody.
Alicia: Didn't you tell me to go ahead?
Devlin: A man doesn't tell a woman what to do. She tells herself. You almost had me believing in that little hokey-pokey miracle of yours. If a woman like you could ever change her spots.
Alicia: Oh, you're rotten.
Devlin: That's why I didn't try to stop you. And the answer had to come from you.
Alicia: I see. Some kind of love test.
Devlin: That's right.
Alicia: Well, you never believed in me anyways so what's the difference.
Devlin: Lucky for both of us I didn't. It wouldn't have been pretty if I believed in you. If I'd figured: 'She'll never be able to go through with this. She's been made over by love.'
Alicia: (She hides her pain, anguish and tears in her eyes from him by viewing the race through a pair of binoculars.) If you only once had said that you loved me. Oh, Dev.
Devlin: Listen. You chalked up another boyfriend. That's all. No harm done.
Alicia: I hate you.
Devlin: There's no occasion to. You're doing good work. Number 10's out in front. It looks as if Sebastian knows how to pick 'em.
Alicia: Is that all you have to say to me?
Devlin: Dry your eyes baby. It's out of character. Keep on your toes. There's a tough job around. Snap out of it. Here comes dreamboat.

Alex approaches through the crowd and strolls over, and Alicia quickly regains her composure. Alex tells her that he has been watching her from afar through his field glasses. He is concerned that she is attentive and in love with the good-looking Mr. Devlin. She denies it: "Don't talk like that. I detest him...Alex, I've told you before. Mr. Devlin doesn't mean a thing to me." Alex jealously believes that Alicia clearly loves Devlin and cannot hide the fact: "I'd like to be convinced. Would you maybe care to convince me, Alicia, that Mr. Devlin means nothing to you?" He hints that he wants an affirmation of love (acceptance of a marriage proposal) to prove him wrong.

In the Embassy, Prescott is pleased that their "theatrical plan is working." They have learned that Professor Wilhelm Otto Rensler ("one of Germany's scientific wizards" known as "Dr. Anderson") is "experimenting" in Sebastian's house in Brazil. Suddenly, a surprise visit to the Embassy by Alicia is announced. Devlin's reaction and feelings about her impending arrival are initially hidden - his back is to the camera and to the conversation as he stares out a window. Both Prescott ("I don't like her coming here") and Mr. Walter Beardsley (Moroni Olsen) worry about "a woman of that sort." Devlin turns and confronts Beardsley [the only instance (except in the final scene) in which Devlin defends Alicia's soiled reputation - but it is in her absence]. Devlin perfectly articulates the contradictory nature of Alicia's patriotic duty - to not be a lady - with a deeply ironic comment:

Devlin: What sort is that, Mr. Beardsley?
Beardsley: Oh, I don't think any of us have any illusions about her character, have we Devlin?
Devlin: Not at all, not the slightest. Miss Huberman is first, last, and always not a lady. She may be risking her life, but when it comes to being a lady, she doesn't hold a candle to your wife, sir, sitting in Washington playing bridge with three other ladies of great honor and virtue.
Prescott: Take it easy, Dev.

Thinking his remarks are "uncalled for," Devlin is forced to withdraw them and apologize as Alicia enters the room. The embassy officials are "worried" that she is visiting the office. She tells Prescott, Devlin, and the others that she is sorry that she had to "break the rules" but she couldn't find Devlin and needs immediate counsel for "something rather confusing." Sebastian wants to marry her "right away" and she must provide an answer to him at lunch. Alicia is willing to acquiesce to the agency's wishes to marry Sebastian. Devlin conceals his stunned reaction from his place at the window:

Alicia: I didn't know what the department might think about such a step.
Prescott: Are you willing to go this far for us, Miss Huberman?
Alicia: Yes, if you wish.
Prescott: What do you think of this, Devlin?
Devlin: Oh, I think it's a useful idea.
Prescott: Well, you know the situation better than any of us.
Devlin: May I ask what inspired Alex Sebastian to go this far?
Alicia: He's in love with me.
Devlin: And he thinks you're in love with him?
Alicia: Yes, that's what he thinks.

With a pained expression on her face and a glance toward Devlin, Alicia asks one more time for reassurance if it's all right: "Then it's all right?" Devlin, who thought it "a useful idea," does not stop her or answer her question. She is assured by Prescott that her marriage is officially sanctioned - "Of course, it's a perfect marriage - for us." While Devlin sneers that Alex Sebastian, known as being "a very romantic fellow," will demand a long honeymoon for his bride and delay their undercover mission, Prescott is confident that she will return quickly: "I think we can rely on Miss Huberman to get back into the house quickly." Devlin excuses himself, feeling sadly lost and dispensable now that everything is "nicely arranged." Calculatedly, Prescott believes "everything has been managed with great intelligence."

Alex consults with his viperish mother about marriage - and soon is arguing with his domineering mother (in the foreground). She justifiably feels betrayed by her son's impending marriage and objects to his private marriage plans with a scheming Alicia whose intention was solely to come to Rio "to capture the rich Alex Sebastian for a husband." He complains about his mother's "carping questions" about Alicia and defies his Oedipally-inclined mother. Furious, he accuses her of being jealous "just as you've always been jealous of any woman I've ever shown any interest in," and proceeds with his marriage plans despite his mother's displeasing objections. After Alicia and Sebastian are married, their limousine returns them from their brief honeymoon to his darkened, uncheerful estate outside Rio. He apologizes to Alicia for the lack of a "bright homecoming" upon his return, when he learns that his mother is sulking in her bed.

The next day, as Alicia unpacks all her belongings in her room, she asks for the key to one of the locked storeroom closets and is upset to learn from the butler Joseph (Alex Minotis) that Mme. Sebastian, a maternally powerful figure, is in charge of all the house keys. [Keys symbolize instruments that allow one to explore, invade, and violate privacy.] Alicia interrupts Sebastian in a business meeting behind closed doors and asks for the keys. Alex accompanies her upstairs to his mother's room to get the keys. She eavesdrops in the hallway, hearing him argue with his mother (behind another closed door) to relinquish them. Alex unsuspectingly gives them to Alicia - who then proceeds to betray him. With Joseph, she is able to open up every door lock except the one (labeled UNICA) to the wine cellar - "Mr. Sebastian has the key for this Madame." She becomes suspicious of the contents of the one place where she is forbidden.

In a short scene on a city park bench, one of the few fleeting meetings that their doomed romantic relationship allows them to have, Alicia meets with a sarcastic Devlin. Neither of them express their true feelings for each other. She tells him about the locked wine cellar. When she shows concern about how to get the wine cellar key, he cruelly remarks: "Don't you live near him?" When she also asks what to look for after obtaining the key, he recalls the suspicious behavior over a bottle of wine at the dinner party: "You look for a bottle of wine like the one that rattled the fellow at dinner that night." Unyielding to any true articulation of his love for her [his 'horrid passion'], he suggests that she persuade her husband to throw a party for two purposes - so that he can help her investigate the wine cellar - and so that they can disprove their love to Sebastian:

Alicia: All the bottles look alike to me. I'm no mastermind.
Devlin: You're doing all right.
Alicia: It's no fun there.
Devlin: Too late for that now, isn't it? Look, uh, why don't you persuade your husband to throw a large shindig, so that he can introduce his bride to Rio's society, say sometime next week?
Alicia: Why?
Devlin: Consider me invited, and I'll try and find out about that wine cellar business.
Alicia: I don't think my husband is interested in entertaining just yet.
Devlin: The honeymoon isn't over, huh? Don't underestimate your charms, Mrs. Sebastian, you can handle it.
Alicia: I don't think it's gonna be so easy about you. He thinks you're in love with me.
Devlin: Well, then, tell him you thought if you invited me to the house and I saw how happily married you were, then the horrid passion I have for you might be torn out of me.
Alicia: That sounds very logical.
Devlin: Good, next week then, and get the key. I have to fly up to Berlin, but I'll be back in time.

In a suspenseful, tense scene, while preparing for the party at the mansion given in the bride's honor, Alicia removes the key to the wine cellar from Sebastian's key chain without being noticed, as he speaks to her from inside the bathroom. He emerges in his bathrobe from the bathroom and runs after Alicia, grabbing both her hands, and opening and kissing one of them. Then, as he goes to open the other hand (that holds the key), Alicia passionately throws her arms around Sebastian in an embrace, thus preventing him from discovering the key by masking her deception with a gesture of love. She drops the key to the rug behind him, and pushes it away with her foot to hide it until she can retrieve it later.

In the memorable champagne party and wine cellar scenes, Alicia's investigation centers around an apparently innocent wine bottle locked in the wine cellar, where it is believed Alex keeps some special ingredient. With a camera mounted on an enormous crane, Hitchcock starts with an extreme wide-angle shot of the elaborate formal party - above a shimmering chandelier, then gliding down the curving stairway, slowly descending into an extreme closeup of Alicia's tightly clenched fist with the stolen key to the all-important wine cellar in it.

When Devlin arrives as one of the guests - to Alex's jealous consternation - Alicia allows him to kiss her hand, whereby she passes him the key to the wine cellar. As they pretend to enjoy meeting each other with small talk while hiding their own conspiracy, Devlin is understandably concerned about Alex's watchful eye, and foreshadows the depletion of wine and/or champagne at the party:

Devlin: It's kind of your bride to invite me.
Alex: We both invite you, Mr. Devlin. Will you see that our guest is fed, my dear? Amused?...
Devlin: This isn't going to be easy.
Alicia: Why?
Devlin: He, uh, he's quite sensitive about you. He's gonna watch us like a hawk.
Alicia: Yes, he's rather jealous of anyone.
Devlin: Where'd you get the key? Off his chain?
Alicia: Yes.
Devlin: Let's hope the liquor doesn't run out and start him down the cellar for more.
Alicia: Oh, I hadn't thought about that.
Devlin: Quite a point.

[Hitchcock's cameo is inserted here - the director stands at a table, knocks down a glass of champagne, and leaves as they approach.] They both try to estimate how much time and liquor is left before the servants have to get more replacement bottles from the cellar. One by one, champagne bottles are used up as the suspense builds. Alex jealously watches Devlin and Alicia from many vantage points, trying to determine the real nature of Alicia's feelings for him while fantasizing about her betrayal. Devlin expresses his own form of jealousy and displays his distaste for Sebastian's possessiveness. According to Alicia, Devlin has "tried to drown his sorrow." [Remember however, that the motive for the party was so that the spurned Devlin would be cured of his "horrid passion" for Alicia by seeing how happy she was with Sebastian.]

At the first opportune moment, Alicia and Devlin slip into the cellar with the key to snoop and search without being detected. While she waits by the outer garden door to alert him to anyone coming, Devlin discovers the incriminating evidence while looking over the stock. He accidentally breaks a bottle of fine Pommard wine, discovering a black sand/ore (uranium ore, an important ingredient for making atom bombs) hidden inside. Devlin calls it "vintage sand," or "some kind of metal ore." He takes a sample, cleans up the spill the best he can, and substitutes another bottle to leave everything as he found it. Alicia is "terrified" by the spilled evidence.

Just as they leave, the suspicious Alexander with his butler Joseph walk toward the cellar to get more champagne. Alicia hears them coming down the stairs and takes Devlin through a back door to the garden. Alex discovers their presence when he notices them by the garden door. To avoid further suspicion, to cover up the real reason they are there [furtive espionage rather than furtive romancing], and to express his complex love for her, Devlin forces himself on Alicia. He grabs and kisses her. He asks her to pretend in a charade that they are lovers having a love tryst - for Alex's voyeuristic pleasure:

Alicia: Alex, he's seen us.
Devlin: Wait a minute, I'm gonna kiss you.
Alicia: No, he'll only think we - No...
Devlin: It's what I want him to think.

Alicia is overwhelmed by fear and pained by the genuine emotion of kissing Devlin. As Alex opens the garden door, Devlin instructs Alicia: "Push me away." Catching them in the midst of a kiss, Alex tells them: "I'm sorry to intrude on this tender scene." Alicia blames their passion on Devlin's drinking: "I couldn't help what happened. He's been drinking." Alex rightfully concludes that they love each other: "You love him." Trying to explain to the over-jealous Alex that their affair is finally over, Devlin supports Alicia's apology and actually espouses his own previous affection for her:

For what it's worth as an apology, your wife is telling the truth. I knew her before you, loved her before you. But I wasn't as lucky as you.

After Devlin leaves, Alicia denies any further emotional responsibility for what he witnessed: "Alex, don't be foolish. I-I came down because he threatened to make a scene...I couldn't stop him. I tried." This is the film's turning point: Alex' eyes cannot betray what he saw: "He kissed you." Soon after, as Alex descends to the cellar with Joseph to again get more liquor to replenish the supplies, he realizes, in a gigantic close-up, that the wine cellar key is missing from his key ring. Later that evening after the party has ended, Alex smooths over the incident and apologizes to Alicia for "behaving like a stupid schoolboy" - he expresses his understanding of her romantic indiscretion: "It isn't worth mentioning again."