Nicole Beaumont is staring at an invitation from her neighbors, Ted and Maryanne Miller, to a pool party to kick off the summer season. As she looks at the date on the invitation, she realizes that her husband, Jack, will still be on another of his extended business trips to Los Angeles. Jack is a lawyer, a very successful lawyer, and he spends more time on the road than he does at home. Although Nikki is an attractive woman, Jack's career and his monetary success are the driving forces in his life. His physical interest in his wife has waned to the point where their love life is virtually nonexistent.
Whenever Nikki asks Jack to interrupt his travels to spend time with her, he lectures her about the importance of travel to his business and to his ability to provide Nikki with a beautiful home, a pool, a BMW, jewelry, and other trappings of success. Nonetheless, she calls him that evening and virtually begs him to come home for the Millers' party. He brusquely rejects her request.
Nikki calls Maryanne to RSVP her "regrets," but Maryanne won't take "No" for an answer. Maryanne is Nikki's best friend, a gorgeous and successful professional whose husband is a professional photographer and videographer, and every woman's secret fantasy. Maryanne is Nikki's closest confidante and she is aware of the problems in the Beaumonts' marriage. She persuades Nikki to come to the party and allow herself to have a good time.
The party is a gala affair with plenty of good food and good conversation. After cocktails and dinner, Ted announces that the pool and spa are open for business. By the time all of the other guests have left, Nikki is alone in the spa with Ted and Maryanne. Before long, Nikki is sitting on Ted's lap and Maryanne is encouraging her to kiss him. Maryanne then invites Nikki to sit on her lap and kiss her. Although she regards herself as heterosexual, Nikki has long harbored a secret desire for Maryanne. Now, under the moon, in the warm water, fueled by several cocktails, Nikki abandons all inhibition. She kisses Maryanne with a fervor that transcends friendship, slides her hand under the bra of Maryanne's bikini, fondling her lovingly, and asks if she can spend the night. They exit the spa and head for the Millers' bedroom, where Nikki Beaumont engages in the first threesome of her life, a sexual "round robin" of lust and love that stands in marked contrast with the hollow shell of her marriage to Jack.
Before turning in for the night, Nikki asks if her friends would like another drink. They ask her to mix them each a martini. As she does so, she makes herself a greyhound and returns to the bedroom where they drink a toast to their evening. Nikki heads to the shower and, when she is finished, she climbs into bed between Ted and Maryanne, who are asleep. Nikki falls asleep thinking about the morning and how her future will play out with the Millers.
But there is no future. When Nikki awakens, Ted and Maryanne Miller are dead.