Bill and Alice Harford (Tom Cruise
and Nicole Kidman
) are a wealthy professional couple living in Manhattan whom have been married for nine years. He is a doctor with his own private practice and she is unemployed though she has managed an art gallery in the past. They have a seven-year-old daughter, named Helena (Madison Eginton
), whom they leave with a babysitter for the evening. They attend a Christmas party thrown by wealthy attorney Victor Ziegler (Sydney Pollack
). While Bill flirts with two skinny models, Alice dances and flirts with an unctuous middle-aged Hungarian businessman (Sky Dumont). He attempts to seduce her but she declines because she is married. While at the party, Bill runs into an old friend, Nick Nightingale (Todd Field
), a pianist who tells him to come see him at another gig. Suddenly, Bill is called into Ziegler's private upstairs bathroom for an apparent emergency.
Ziegler had been partying with an escort, Mandy (Julienne Davis
). When she shot up a mixture of heroin and cocaine, she passed out, scaring Ziegler. Bill rouses her back to consciousness then chides her about getting into rehab. Ziegler makes Bill promise not to mention the incident to anyone.
Alice is troubled by their individual flirtations with other people at the party. The next night, she rolls a joint and they both get stoned. She asks Bill if he had sex with the models the previous night. He denies it but asks about the man she had been dancing with. She says he wanted to have sex with her, which Bill says is understandable. Alice interprets this to mean that she would only be interesting to men if they wanted to have sex with her and begins a discussion about fidelity and sex drives. When Bill claims that women require love before they can have sex and that he has never been concerned she would cheat on him, Alice laughs. She tells him about a fantasy she has had about throwing away her married life in exchange for cheap sex with a naval officer she once saw in a restaurant while with Bill. Their discussion comes to a sudden end when Bill is called away on a house call, but he is troubled by visions of Alice being ravished by the faceless naval officer.
The house call is to attend to a patient who just died. The patient's daughter, Marion (Marie Richardson
), confesses to Bill that she is deeply in love with him and needs to be near him, even if she will never get to see him. Bill politely declines her advance, telling her that she is distraught and confused by her father's death. Marion's boyfriend Carl (Thomas Gibson
) arrives which makes Bill leave.
Walking home, Bill sees a hooker making out with a john and continues to be plagued by images of his wife being unfaithful. Minutes later, a group of drunken young college men attack Bill and shove him down on the street and accuse him of being gay for no reason.
Another few minutes later, a prostitute named Domino (Vinessa Shaw
), propositions him, he reluctantly agrees. Bill and Domino go to her apartment but before they can have sex, Alice calls on his cell phone. He lies that he is still at the patient's house but is unable to go through with the session after hanging up.
Continuing his walk, he passes the Sonata Club, where his former medical school chum, Nick Nightingale, is playing piano with a group. Bill decides to stop in to listen. After the music number is up, Nick meets with Bill for drinks at a table. He reveals that he is scheduled to play piano at a sex party later that night and he is waiting for the code word. When Nick takes the phone call on his cell phone telling him where the party will take place and the code word, Bill hectors him for more details -- he wants to attend. Nick reveals the code word and that the orgyists wear costumes. Nick says he's not sure because he's always blindfolded when he plays at the parties.
Even though it is after 1:00 a.m. in the morning, Bill walks to a costume shop called "Rainbow Fashions" having been the doctor of the previous owner. He offers the new owner, a middle aged European man named Mr. Milich (Rade Serbedzija
) a generous amount of money to rent to him now. In the search for a costume, the owner catches his teenage daughter (Leelee Sobieski
), clad in only her underwear, cavorting with two older Japanese men in a back room. Mr. Milich chases them out and expresses outrage at their lack of sense of decency. He threatens to call the police after he has served Bill.
On the way to the party in taxi, Bill continues to fantasize about his wife with the naval officer. Using the password supplied by Nick, he gains access to the party, held at a remote mansion on Long Island. The party features cloaked and mask-clad men and women performing quasi-religious pagan like rituals of pornographic nature, before retiring to watch or participate in a variety of sexual acts in other rooms through the mansion. Nick is seen, blindfolded, playing an electric organ. One masked woman comes to Bill, takes him aside and warns him that he does not belong there.
A few minutes later, Bill meets another masked girl in whose company he walks through a few rooms where an orgy is taking place. The first masked woman catches up with Bill and insists he is in terrible danger for the others suspect that he is an outsider. Bill asks the woman her name and why she is telling him this, but she refuses to answer and tells him to leave. Bill refuses and tells the masked woman to leave with him, but she again refuses saying that it could cost her life and maybe his. Bill is then interrupted by a masked porter who tells him that the taxi driver who is waiting outside wants to speak with him. However, the porter takes him to the main room where the masked, red-cloaked Master of Ceremonies confronts Bill with a question about a second password which Bill is unable to answer. The Master of Ceremonies insists that he "kindly remove his mask", then asks that he remove his clothes. The just then, the young nudable woman who had tried to warn Bill now intervenes and insists that she be punished instead of him. As she is taken away, Bill asks what is going to happen to her. The Master cryptically replies her fate is sealed. Bill is allowed to leave, but he is also warned not to tell anyone about what happened there or he and his family will suffer dire consequences..
Bill returns home at dawn, guilty and confused. He hides the costume in a locked bureau in his office. Alice is now awake and tells him of a troubling dream in which he and she were in a deserted city without their clothes. She felt frightened and ashamed while he went off to try to find their clothes. After he left, she felt better, finding herself, still naked, in a beautiful garden. The naval officer emerged, stared at her, and the two of them began making love surrounded by many other couples doing the same. She then started having sex with many of those men and laughing at the idea of him seeing her with them.
The next morning, Bill goes to a restaurant next door to the Sonata cafe in search of Nick Nightingale where he learns from the waitress and countergirl where Nick is staying. Bill goes to the hotel to see if Nick is all right, and he learns from the front desk clerk (Alan Cumming
) that Nick checked out a few hours ago at around 5:00 a.m. When Bill asks the desk clerk if there was "anything odd" about the way Nick checked out, the desk clerk tells Bill that Nick returned to the hotel just before dawn at about 4:30 a.m. and he was accompanied by two well-suited, burly, well-spoken but rough-looking men, one of whom went up to his room with Nick while the other paid for his hotel bill. When Nick came back downstairs with the other man to check out and hand in his room key, the desk clerk tells Bill that Nick tried to pass an envelope to him, but one of the men noticed this and he intercepted and took it away before Nick could tell him what to do with it. The two men then appeared to forcibly take Nick and his luggage into a waiting limousine parked outside the hotel and was driven away by with the two men, with no mention as to where they were going. The desk clerk also tells Bill that Nick also appeared to be frightened, and he also had one or more bruises on his face which may have been the cause of being beaten up.
A little later that day, Bill goes to return the costume to Rainbow Fashions, but the mask is missing. So the proprietor, Milich, adds the missing mask to Bill's charge. Milich's daughter and the two Japanese men appear again for a few seconds before leaving. Milich's daughter is still in her underwear, but her flirty demeanor towards Bill is replaced by a glassy stare. With his daughter by his side, Mr. Milich states he can do other favors for Bill "and it needn't be a costume". Milich now makes clear to Bill that he pimps his daughter and implies that he may have sold her to the Japanese businessmen.
More disturbed then ever, Bill returns to the site of the party, where he is given a note at the front gate... addressed to him. Although the people there saw his face, he had never told anyone at the party his name. The note tells Bill to stop trying to learn more about the previous night's events and to not only stay away, but stay quiet about what happened and to consider the note his "second warning".
Though the rest of the day, Bill cannot get Alice's dream of orgiastic infidelity out of his head. After Bill returns home from work, he thinks about Alice's recounting of the scene while he watches her instruct her daughter in math. After dinner, Bill lies to Alice about having appointments at his office that very night night. He goes to see Domino but when she is not home, he tries to seduce Sally, Domino's roommate (Fay Masterson
). Instead she tells him that Domino has disappeared after learning she is HIV-positive. Bill then attempts to call Marion, but hangs up when her boyfriend, Carl, answers the phone.
Walking down a street, brooding, Bill sees that a well-dressed stranger is following him from across the street. Bill ducks into a nearby coffee shop and apparently loses his pursuer. There, Bill reads an article from a discarded newspaper, the New York Post, that Mandy, a former beauty queen, was found dead of a drug overdose in a hotel room that morning. Using his doctor's credentials, Bill goes to the morgue to confirm the body is hers. He realizes that Mandy was the woman he attended to at the Christmas party two nights earlier because of her drug overdose, and she was also the same masked woman who tried to warn him during the orgy and Bill now fears that she died to protect him.
As he is leaving the hospital, Bill receives a call on his cell phone from Ziegler who wants to meet with him. In Ziegler's apartment, he pleads with Bill to stop trying to find out more about the orgy and investigating the secret society that held it. Ziegler was one of the attendees himself and saw everything that happened at the party. Ever since then, Ziegler was the one who had Bill followed because his own position with the group has been jeopardized by Bill's intrusion thanks to Nick telling Bill about the event. Ziegler tells Bill that beyond voyeurism and sex, nothing untoward happened at the party. All of the warnings and the trial, Ziegler suggests, were staged to frighten Bill into keeping quiet.
The people who held the party are important, powerful people who want to protect their privacy, Ziegler tells Bill. They found Bill and his identity out because of his own sloppiness (Bill showing up in a taxi whereas everyone else showed up in limousines, plus the receipt for the costume rental was found in his coat pocket), and not through any evil or supernatural designs. On top of that, Ziegler tells Bill that the second password he was asked never existed for it was only a ruse to trick Bill into revealing his status as a trespasser. Bill is now concerned with the death of Mandy, whom Ziegler has identified as the woman at the party as well as the same woman from the orgy who "sacrificed" herself to prevent Bill's punishment, as well as the disappearance of Nick. Ziegler claims that Nick is safely back in Seattle (but doesn't know where to get ahold of him), and Mandy wasn't killed to save Bill. She was simply a prostitute who had a bad drug problem and she indeed died from an accidental drug overdose and there was no foul play at all by stating "life goes on". Bill clearly does not know if Ziegler is telling him the truth, but he accepts it anyway.
Bill returns home. He finds his mask from the orgy lying on his pillow next to a sleeping Alice. He breaks down and tells her everything. Alice cries over what she hears. The next morning, Bill and Alice take their daughter Christmas shopping at a local store. In a private moment, Bill asks Alice what they should do about their problems. She is grateful that they have both survived their recent real-life and dream-life flirtations with infidelity, but stops short of promising eternal love and faithfulness on her part.
In the meantime, she suggests, they should get home and "fuck" as soon as possible.