Three middle-class married couples — Jack Burroughs [Alan Alda], Kate Burroughs [Carol Burnett]; Nick Callan [Len Cariou], Anne Callan [Sandy Dennis]; Danny Zimmer [Jack Weston], Claudia Zimmer [Rita Moreno] — live in New York City and are the best of friends. Jack is a moralistic lawyer, Kate a Fortune magazine editor, Nick an insurance salesman and estate planner, Anne a housewife and photographer who enjoys taking pictures of vegetables, Danny a cheap dentist who displays symptoms of obsessive-compulsive disorder and hypochondriasis, and Claudia an insensitive Italian painter. Quarterly (in each of the four seasons), the three couples go on vacations planned by Kate.
Spring
In May, the six friends retreat to Nick's and Anne's weekend cottage in the forest to celebrate Nick's and Anne's anniversary. The husbands cook Chinese food and race bikes, while the wives discuss Anne's latest photos. While gathering firewood, Nick opens up to Jack about his unhappiness in his marriage and his plan to divorce Anne, hoping to find a woman who can excite him. When Jack asks if another woman is involved, Nick denies it. That night, Kate is devastated when Jack shares Nick's intentions, and both worry about Anne’s future.
Summer
Nick has separated from Anne and is dating Ginny Newley, a younger, beautiful, naive woman. The Burroughses and the Zimmers don’t approve of the daily gifts and Ginny’s credulous belief in Nick’s stories. All three couples, except Anne, spend the summer in a sailboat cruising around St. Thomas. During the voyage, the sailboat runs aground on a sandbar, and the group struggles to sleep as Nick and Ginny’s loud nighttime trysts echo through the hull. Once the boat is freed and the journey resumes, the Burroughses privately discuss how Nick and Ginny’s relationship is affecting everyone. After seeing Nick and Ginny swimming naked, the Zimmers decide to imitate them in the sea.
Autumn
In fall, the group heads to Connecticut for Parents’ Weekend with their daughters Beth Burroughs and Lisa Callan. Checking into the university inn, they awkwardly encounter Anne, who is there to spend time with Lisa. Kate and Claudia apologize to Anne for not inviting her on previous vacations, insisting that Nick would always bring Ginny along. Anne, depressed by the separation, reveals she’s trying new things, like a vacation in Czechoslovakia and adopting a pet snake. Beth confides that despite being childhood friends, she and Lisa have grown apart. Meanwhile, Danny grows increasingly upset with Claudia’s insensitivity toward others, a trait she defends as part of her heritage and refuses to apologize for. Nick, meanwhile, is exposed as a womanizer, with Anne learning of his infidelity. During a soccer game, Jack injures his knee while tackling Nick, fueling their estrangement. That night, the Burroughses clash over Nick and Ginny, and Kate confesses she hates planning the quarterly vacations.
Winter
The Callans divorce, Nick marries Ginny, and Anne has become a magazine photographer. At a ski resort, the three couples rent a lodge and a skiing match between Nick and Jack ends with Nick breaking an ankle while Jack tears a ligament. To lift spirits, Ginny invites everyone to a bar, where Danny’s friends mock his irrational fears about his health. Ginny defends him, surprising the group. Back at the lodge, Kate insults Ginny by saying she’ll never truly belong with them, prompting Ginny to leave in anger. Nick reveals that Ginny is pregnant, which adds another layer of tension. The group erupts again, culminating in Jack vandalizing furniture before Kate settles the dispute. When Ginny does not return the next morning, Danny sets out to find her. He discovers her jogging, but he trips and falls through thin ice. Ginny hurries back to the lodge to alert the others, and they race to Danny in his Mercedes-Benz to save him; the car plunges through the ice and sinks into the freezing water. The retreat ends with a reconciliation as they walk back to the lodge, and Kate quips that perhaps they should return to the resort next winter.
