A third older couple sit on the love-seat and describe the convoluted path to their successful second marriage after their first marriage of three years ended in a five year-long divorce: (It is actually his fourth attempt at marriage after two other divorces.)

Man: We were married forty years ago. We were married three years. We got a divorce. Then I married Marjorie.
Woman: But first you lived with Barbara.
Man: Right. Barbara. But I didn't marry Barbara. I married Marjorie.
Woman: Then, you got a divorce.
Man: Then I married Katie.
Woman: Another divorce.
Man: Then, a couple of years later at Eddie Callichio's funeral, I ran into her. I was with some girl I don't even remember.
Woman: Roberta.
Man: Right, Roberta. But I couldn't take my eyes off you. I remember, I snuck over to her and I said - what did I say?
Woman: You said, 'What are you doing after?'
Man: Right. So I ditched Roberta, we go for coffee, a month later we're married.
Woman: Thirty-five years to the day after our first marriage.

FIVE YEARS LATER

Sally is seated at a New York restaurant table with two other women who are her friends and confidants: Marie (Carrie Fisher), who regularly dates married men without success, and Alice (Lisa Jane Persky). Sally has just broken up with Joe after "growing apart for quite a while."

Sally: I said to myself, you deserve more than this. You're thirty-one years old...
Marie: ...and the clock is ticking.
Sally: No, the clock doesn't really start to tick until you're thirty-six.
Alice: God. You're in such great shape.
Sally: Well, I've had a few days to get used to it, and, uh, I feel OK.
Marie: Good. Then you're ready.

To assist her best friend, Marie takes out her Rolodex index of available men, but Sally wants to wait until she is over her "mourning period":

Look, there is no point in my going out with someone I might really like if I met him at the right time, but who right now has no chance of being anything to me but a transitional man.

Marie doesn't want Sally to wait too long, or she will miss her opportunity: "I'm saying that the right man for you might be out there right now and if you don't grab him, someone else will, and you'll have to spend the rest of your life knowing that someone else is married to your husband."

At a New York Giants professional football game (in between waves passing through the crowd), Harry despondently tells friend Jess (Bruce 'Bruno' Kirby), his confidant, that his marriage to Helen is dissolving:

Helen comes home from work, and she says, 'I don't know if I want to be married anymore.' Like it's the institution, you know, like it's nothing personal, just something she's been thinking about in a casual way. I'm calm. I say, 'Why don't we take some time to think about it?' You know, don't rush into anything...Next day, she says she's thought about it, and she wants a trial separation. She just wants to try it, she says. But we can still date, like this is supposed to cushion the blow. I mean, I got married so I could stop dating, so I don't see where 'we can still date' is any big incentive, since the last thing you want to do is date your wife, who's supposed to love you, which is what I'm saying to her when it occurs to me that maybe she doesn't. So I say to her, 'Don't you love me anymore?' and you know what she says? 'I don't know if I've ever loved you.'

As a writer, Jess explains how that was a very 'harsh' comment to be told. Harry explains how he found out that his wife had planned to move out all along - at least a week earlier, because she had hired movers (one of whom had a T-shirt emblazoned with: "Don't F--K with Mr. Zero") who had been notified, but he wasn't told - because she didn't want to ruin his birthday:

Jess: You're saying Mr. Zero knew you were getting a divorce a week before you did?
Harry: Mr. Zero knew.

Harry's wife is moving out - and the pretense of her subleting someone's else's apartment for a trial separation was a lie, according to Harry. "She's in love with somebody else, some tax attorney. She moved in with him." Disillusioned and cynical about his marriage, Harry feels he's been used and humiliated:

Harry: I knew the whole time that even though we were happy, it was just an illusion and that one day she would kick the s--t out of me.
Jess: Marriages don't break up on account of infidelity - it's just a symptom that something else is wrong.
Harry: Oh really? Well, that symptom is f--king my wife.

Harry and Sally meet again, their third encounter. This time, they cross paths in the Shakespeare and Co. Bookstore - he is staring at her from the Personal Growth section, while nearby she is conversing with Marie (who quickly gives them room to talk by exiting down the stairs), and grasping a book titled Smart Women Foolish Choices: Finding the Right Men, Avoiding the Wrong Ones. It has been ten years since their overnight drive from Chicago to New York. After learning that she has broken up with Joe, and that he is in the midst of a divorce to Helen [that's presumably the reason he is browsing in the 'Personal Growth' section'], the two decide to have coffee together in a restaurant and talk about their ill-fated relationships. There, she discusses her lack of commitment to Joe, and how the issue of sex is eliminated when a couple gets married:

Sally: When Joe and I started seeing each other, we wanted exactly the same thing. We wanted to live together, but we didn't want to get married because every time anyone we knew got married, it ruined their relationship. They practically never had sex again. It's true, it's one of the secrets that no one ever tells you. I would sit around with my girlfriends who have kids - and, actually, my one girlfriend who has kids, Alice - and she would complain about how she and Gary never did it anymore. She didn't even complain about it, now that I think about it. She just said it matter-of-factly. She said they were up all night, they were both exhausted all the time, the kids just took every sexual impulse they had out of them. And Joe and I used to talk about it, and we'd say we were so lucky we have this wonderful relationship, we can have sex on the kitchen floor and not worry about the kids walking in. We can fly off to Rome on a moment's notice. And then one day I was taking Alice's little girl for the afternoon because I'd promised to take her to the circus, and we were in the cab playing 'I Spy' - I spy a mailbox, I spy a lamp-post - and she looked out the window and she saw this man and this woman with these two little kids. And the man had one of the little kids on his shoulders, and she said, 'I spy a family.' And I started to cry. You know, I just started crying. And I went home, and I said, 'The thing is, Joe, we never do fly off to Rome on a moment's notice.'
Harry: And the kitchen floor?
Sally: Not once. It's this very cold, hard Mexican ceramic tile. Anyway, we talked about it for a long time, and I said, this is what I want, and he said, well, I don't, and I said, well, I guess it's over, and he left. And the thing is, I-I feel really fine. I am over him. I mean, I really am over him. That was it for him, that was the most that he could give, and every time I think about it, I am more and more convinced that I did the right thing.

As they walk along the park, their relationship has matured. "It Had to Be You" plays softly on a piano, and they discuss their first meeting:

Harry: You know, the first time we met, I really didn't like you that much -
Sally: I didn't like you.
Harry: Yeah you did. You were just so uptight then. You're much softer now.
Sally: (She stops and puts both hands on her waist) You know, I hate that kind of remark. It sounds like a compliment, but really it's an insult.
Harry: OK, you're still as hard as nails.
Sally: I just didn't want to sleep with you, and you had to write it off as a character flaw instead of dealing with the possibility that it might have something to do with you.
Harry: What's the statute of limitations on apologies?
Sally: Ten years.
Harry: Ooh. I can just get it in under the wire.

Even though both realize the potential dangers of "becoming friends," Sally asks Harry if he would like to have dinner with her sometime. Harry quips:

Great. A woman friend. You know, you may be the first attractive woman I've not wanted to sleep with in my entire life.

A fourth interlude shows an elderly couple (talking over and finishing each other's lines with similar comments) who remember how they were both born in the same hospital in 1921, seven days apart, and grew up one block away from each other. They both lived in tenements on the Lower East Side on Delancey Street, and later moved to the Bronx, where they would ride the same elevator up to work but never met. But they did meet in an elevator in the Ambassador Hotel in Chicago while visiting family. The man remembers: "I rode up nine extra floors just to keep talking to her."

The next sequence presents a montage of images while Harry and Sally talk on the phone (in voice-over) in late-night marathon conversations. At work, Harry stares at his toy bird dunking its beak into a glass of water; Sally is also busy at a computer work terminal and a fussy eater as she serves herself from a supermarket salad bar; a depressed and pathetic-looking Harry in his vacant apartment tosses playing cards into a bowl about ten feet away; and Sally vigorously takes a tap-dancing class. In a Chinese restaurant, Sally and Harry order dinner together, and later, he stands impatiently behind her as she mails letters at a mailbox on the street.

Before the split-screen scene of their watching the last scene of Casablanca (1942), the voice-over dialogue at the start of that scene (but during the previous montage of images) is about how they each identify with the characters in the film, as they did years earlier during their long road-trip. Sally denies ever having said that she preferred the practical choice - Victor Laszlo over Rick. Harry maturely yields to Sally's insistence, even though his memory is correct:

Harry: Now you're telling me you would be happy with Victor Laszlo than with Humphrey Bogart.
Sally: When did I say that?
Harry: When we drove to New York?
Sally: I never said that. I would never have said that.
Harry: All right, fine, have it your way.

In a split-screen effect, as both watch the film together on television - while reclining in bed in their own apartments, but they maintain a conversation about the film on the phone:

Harry: There are two kinds of women: high maintenance and low maintenance.
Sally: And Ingrid Bergman is low maintenance?
Harry: An L.M. Definitely.
Sally: Which one am I?
Harry: You're the worst kind. You're high maintenance, but you think you're low maintenance.
Sally: I don't see that.
Harry: You don't see that? (He mimics her typical ordering procedure) 'Waiter, I'll begin with the house salad, but I don't want the regular dressing. I'll have the balsamic vinegar and oil, but on the side, and then the salmon with the mustard sauce, but I want the mustard sauce on the side.' 'On the side' is a very big thing for you.
Sally: Well, I just want it the way I want it.
Harry: I know, high maintenance. (Sally sighs after Bogart says the final line of the film, when the two characters walk off into the fog-shrouded airport: 'Louis, I think this is the beginning of a beautiful friendship.') Ooh. Best last line of a movie, ever.

Harry and Sally spend more and more time together and their friendship blossoms. In one sequence, they share their deepest fantasies amidst walks. Harry's insecurities are reflected in a recurring dream in which his love-making is judged in the Olympics. "My mother, disguised as an East German judge gave me a 5.6. Must have been the dismount." Sally describes an embarrassing sexual fantasy she has had since puberty - a "faceless guy" rips off her clothes:

Harry: That's it? A faceless guy rips off your clothes, and that's the sex fantasy you've been having since you were twelve? Exactly the same.
Sally: Well, sometimes I vary it a little.
Harry: Which part?
Sally: What I'm wearing. (Harry reacts) What?
Harry: Nothing.

After each have horrible dating experiences, they discuss how "uncomfortable" it is to "get out there." Although Sally encourages Harry with advice: "The first date back is always the toughest," she describes how bad her "dream date" really was:

How much worse can it get than finishing dinner, having him reach over, pull a hair out of my head, and start flossing with it at the table?

Harry relates how his nice date was completely humorless, not laughing at his joke about eating in an Ethiopian restaurant and being awkwardly unable to relate to her. They offer mutual support to each other after traumatic dating:

Harry, I think this takes a long time. It might be months before we're actually able to enjoy going out with someone new...And maybe longer before we're actually able to go to bed with someone new.

Harry provides the punchline of the scene - even though his date was terrible, he admits: "Oh, I went to bed with her" - to Sally's stunned amazement! [His non-chalant comment demonstrates how they, and many men and women, view sex and relationships so differently.] The next discussion that Harry has with Jess during baseball hitting practice provides further commentary on male/female relationships. Harry explains to Jess during baseball hitting practice about the uniqueness of his platonic relationship with Sally - that he enjoys being with Sally and that he finds her attractive, but doesn't sleep with her:

Why can't you give me credit for this? This is a big thing for me. I've never had a relationship with a woman that didn't involve sex. Hey look, I'm growin'....It's very freeing. I can say anything to her...It's a whole different perspective. I get the woman's point of view on things. She tells me about the men that she goes out with and I can talk to her about the women that I see...And the great thing is, I don't have to lie because I'm not always thinkin' about how to get her into bed. I can just be myself.

In the justly-famous restaurant-deli scene [filmed in New York's world famous Katz's Deli], commitment-shy Harry describes how he can "just get up out of bed and leave" after sex by any number of fake excuses: "I say I have an early meeting, an early haircut, an early squash game." Sally is affronted by his insensitivity and sexist attitudes:

You know, I am so glad I never got involved with you. I just would have ended up being some woman you had to get up out of bed and leave at three o'clock in the morning and go clean your andirons. And you don't even have a fireplace...You are a human affront to all women. And I am a woman.

Harry confidently believes his sexual prowess satisfies his female partners and brings them to orgasm, until Sally explains how "most women, at one time or another, have faked it." Harry doesn't believe that he has been fooled because he 'knows':

Sally: Oh right. That's right. I forgot. You're a man.
Harry: What is that supposed to mean?
Sally: Nothing. It's just that all men are sure it never happens to them, and most women at one time or another have done it, so you do the math.
Harry: You don't think that I can tell the difference?
Sally: No.
Harry: Get outta here.

Sally looks at Harry seductively, and begins to illustrate, in the middle of the busy restaurant, how easily women can convincingly fake an orgasm. With a loud and long display of pants, groans, gasps, hair rufflings, caresses, table poundings, and ecstatic releases, she yells: "Yes, Yes, YES! YES! YES!" The entire restaurant is quieted down and attentive to her realistic act. When she is finished with her demonstration, she calmly composes herself, picks up her fork and resumes eating. This is followed by the film's funniest punchline, delivered by another customer (Estelle Reiner - director Rob Reiner's mother) who tells the waitress, "I'll have what she's having" - referring to the meal ordered by Sally. [This scene, very out of character for the normally-repressed and introverted Sally, was filmed late in the production, and was to be used principally as the film's trailer - but then it became the integral, most-remembered scene.]

It is Christmas time in New York City with a montage of beautiful images - a horse-drawn carriage pulling people through Central Park, people bundled up walking through the snow or cross-country skiing, the Rockefeller Plaza Christmas tree and ice skating rink, an animated store window display, children tobagganing and sledding down a hill, tree and light decorated streets, and the outdoor Wollman ice skating rink. Sally negotiates the price for a Christmas tree at a lot and she and Harry carry it to his place. It is New Years' Eve - a champagne bottle is popped open at a party, and Sally and Harry are dancing and dipping together:

Sally: I really want to thank you for taking me out tonight.
Harry: Oh, don't be silly. And next New Years' Eve, if neither one of us is with anybody, you got a date.
Sally: Deal. See, now we can dance cheek to cheek.

As they turn, their expressions show how their platonic feelings are becoming more romantic. After a loud countdown to the New Year, they pause and stare awkwardly at each other, and then give each other a quick peck and a hug. The camera freezes on their embrace - and fades to black. They still insist on keeping their deep friendship and romance mutually exclusive:

A fifth couple presents a testimonial about their first meeting and their instinctive love for each other:

Woman: He was a head counselor at the boys' camp, and I was a head counselor at the girls' camp. And they had a social one night. And he walked across the room. I thought he was coming to talk to my friend Maxine, because people were always crossing rooms to talk to Maxine, but he was coming to talk to me. And he said -
Man: I'm Ben Small of the Coney Island Smalls.
Woman: At that moment, I knew. I knew the way you know about a good melon.

Both Sally and Harry plan to be matchmakers and set up blind dates for each other. They want to introduce each other to their best friends - Marie and Jess - in a West Broadway restaurant, to help jump-start new relationships with different people:

Sally (to Marie): Look, Harry is one of my best friends, and you are one of my best friends, and if by some chance you two hit it off, then we could all still be friends instead of drifting apart the way you do when you get involved with someone who doesn't know you're friends.

On their way to the restaurant, Harry and Jess debate the age-old issue of personality vs. attractiveness:

Jess: When someone's not that attractive, they're always described as having a good personality.
Harry: Look, if you had asked me what does she look like and I said, she has a good personality, that means she's not attractive. But just because I happen to mention that she has a good personality, she could be either. She could be attractive with a good personality, or not attractive with a good personality.
Jess: So which one is she?
Harry: Attractive.
Jess: But not beautiful, right?

Although Jess and Sally, and Marie and Harry are arranged to sit together as couples at the four-person table, they engage in awkward, obviously incompatible conversations with their respective dates. However, both Marie and Jess suddenly become involved with each other after Marie quotes a line from a magazine article he wrote: "Restaurants are to people in the eighties what theater was to people in the sixties." Jess is astonished: "Nobody has ever quoted me back to me before." After the meal, Marie tells Sally how "comfortable" and interested she is in going out with her date. Sally is overly protective of Harry: "I'm just worried about Harry. He's very sensitive, he's going through a rough period, and I-I just don't want you to reject him right now." Harry and Jess have an identical conversation, with Jess asking Harry's permission to call Marie. Harry is concerned about Sally's psyche: "Sally's very vulnerable right now. I mean, you can call Marie, it's fine, but just, like, wait a week or so, you know? Don't make any moves tonight." Hitting it off immediately, both Jess and Marie grab a cab together, leaving the boring Harry and Sally standing together on the street - without regrets for abandoning them.