Robert is a well-liked single man living in New York City, whose friends are all married or engaged couples: Joanne and Larry, Peter and Susan, Harry and Sarah, David and Jenny, and Paul and Amy. It is Robert's 35th birthday and the couples have gathered to throw him a surprise party. When Robert fails to blow out any candles on his birthday cake, the couples promise him that his birthday wish will still come true, though he has wished for nothing, since his friends are all that he needs. What follows is a series of disconnected vignettes in no apparent chronological order, each featuring Robert during a visit with one of the couples or alone with a girlfriend. The first of these features Robert visiting Sarah, a foodie supposedly now dieting, and her husband Harry, an alcohol abuser supposedly now on the wagon. Sarah and Harry taunt each other on their vices, escalating toward karate-like fighting and thrashing that may or may not be playful. The caustic Joanne comments sarcastically that it is "The Little Things You Do Together" that make a marriage work. Harry then explains, and the other married men concur, that marriage changes both everything and nothing about the way you live.
Robert is next with Peter and Susan, on their apartment terrace. Peter is Ivy League, and Susan is a southern belle; the two seem to be a perfect couple, yet they surprise Robert with the news of their upcoming divorce. At the home of the uptight Jenny and chic David, Robert has brought along some marijuana that they share. The couple turns to grilling Robert on why he has not yet gotten married. Robert claims he is not against the notion, but three women he is currently fooling around with—Kathy, Marta, and April—proceed to chastise Robert, Andrews Sisters-style, for his reluctance to being committed. David tries to tell Robert privately that Jenny didn't like the marijuana, after she asks for another joint.
All of Robert's male friends are deeply envious about his commitment-free status, and each has found someone they find perfect for Robert, but Robert is waiting for someone who merges the best features of all his married female friends. Robert meets his three girlfriends in a small park on three separate occasions as Marta sings of the city: crowded, dirty, uncaring, yet somehow wonderful. Robert first gets to know April, a slow-witted airline flight attendant. Robert then spends time with Kathy; they had dated previously and both admit that they had each secretly considered marrying the other. They laugh at this coincidence before Robert suddenly considers the idea seriously; however Kathy reveals that she is leaving for Cape Cod with a new fiancé. Finally, Robert meets with Marta; she loves New York, and babbles on about topics as diverse as true sophistication, the difference between uptown and downtown New York, and how you can always tell a New Yorker by his or her ass. Robert is left stunned.
The day of Amy and Paul's wedding. They have lived together for years, but are only now getting married. Amy is in an overwhelming state of panic and, as the upbeat Paul harmonizes rapturously, Amy patters an impressive list of reasons why she is not getting married. Robert, the best man, and Paul watch as she complains and self-destructs over every petty thing she can possibly think of and finally just calls off the wedding explicitly. Paul dejectedly storms out into the rain and Robert tries to comfort Amy, but emotionally winds up offering an impromptu proposal to her himself. His words jolt Amy back into reality, and she runs out after Paul, at last ready to marry him.
At the birthday party, Robert is given his cake and tries to blow out the candles again. He wishes for something this time, someone to marry him... but just a little.
Robert goes to blow out his candles. This time, he gets them about half out, and the rest have to help him. The couples share their views on Robert with each other, comments which range from complimentary to unflattering, as Robert reflects on being the third wheel, soon followed by the up-tempo paean to Robert's role as the perfect friend.
Robert brings April to his apartment for a nightcap after a date. She marvels ad nauseam at how homey his place is, and he casually leads her to the bed, sitting next to her on it and working on getting her into it. She earnestly tells him of an experience from her past, involving the death of a butterfly; he counters with a bizarre remembrance of his own, obviously fabricated, and designed to put her in the mood to succumb to seduction. Meanwhile, the married women worry about Robert's single and lonesome status (as they see it), and particularly about the unsuitable qualities they find in the women he does date.
The next morning, April rises early, to report for duty aboard a flight to "Barcelona." Robert tries to get her to stay, at first wholeheartedly, parrying her apologetic protestations that she can't, with playful begging and insistence. As April continues to reluctantly resist his entreaties, and sleepiness retakes him, Bobby seems to lose conviction, agreeing that she should go; that change apparently gets to her, and she joyfully declares that she will stay, after all and Robert immediately regrets it.
Robert takes Marta to visit Peter and Susan, on their terrace. Apparently, Peter flew to Mexico to get the divorce, but he phoned Susan and she joined him there for a vacation. Bizarrely, they are still living together, claiming they have too many responsibilities to actually leave each other's lives, and that their relationship has actually been strengthened by the divorce. Susan takes Marta inside to make lunch, and Peter asks Robert if he has ever had a homosexual experience. They both admit they have, and Peter hints at the possibility that he and Robert could have such an encounter, but Robert uncomfortably laughs the conversation off as a joke just as the women return.
Joanne and Larry take Robert out to a nightclub, where Larry dances, and Joanne and Robert sit watching, getting thoroughly drunk. She blames Robert for always being an outsider, only watching life rather than living it, and also persists in berating Larry. She raises her glass in a mocking toast to "the ladies who lunch", passing judgment on various types of rich, middle-aged women wasting their lives away with mostly meaningless activities. Her harshest criticism is reserved for those, like herself, who "just watch," and she concludes with the observation that all these ladies are bound together by a terror that comes with the knowledge that "everybody dies." Larry returns from the dance floor, taking Joanne's drunken rant without complaint and explains to Robert that he still loves her dearly. When Larry leaves to pay the check, Joanne bluntly invites Robert to begin an affair with her, assuring him that she will "take care of him." The negative strikes Joanne as a profound breakthrough on his part. Bobby insists it's not, that he's studied and been open to marriages and commitment, but still questions what do you get. Joanne and Larry go home, leaving Robert lost in frustrated contemplation.
Robert reflects openly enumerating the many traps and dangers he perceives in marriage; speaking their disagreements, his friends counter his ideas, one by one, encouraging him to dare to try for love and commitment. Finally, Bobby's words change, expressing a desire, increasing in urgency, for loving intimacy, even with all its problems, and the wish to meet someone with whom to face the challenge of "being alive."
