Plot
Timid Jonathan McQuarry is an accountant in Manhattan. Late one night, while working on an audit at a law firm, he is befriended by a charismatic lawyer, Wyatt Bose. Taking the subway home, Jonathan has a brief encounter with a blonde woman. Reaching home, he notices a pipe in his bedroom is leaking and leaving a stain.
Jonathan and Wyatt become good friends. Wyatt has business in London for the next few weeks, but accidentally switches cell phones with Jonathan. Jonathan receives a call on Wyatt's phone, from a woman who asks if he is free that night. He impulsively agrees to meet her at a hotel bar. When she arrives, they proceed directly to a hotel room and have sex. In the morning, Jonathan realizes that Wyatt must be in an exclusive sex club.
When Wyatt calls the next day, he encourages Jonathan to continue in the sex club. One encounter is with an older woman, who explains the rules: the initiator pays for the room, no names are exchanged, there is no rough play. Over the next few weeks, he has anonymous sex with several beautiful women.
Jonathan is surprised one evening to find that his latest encounter is the blond woman from the subway. Instead of having sex, they order room service and talk for hours. Jonathan assumes that her name begins with an "S" because of her S-shaped keychain.
Jonathan rejects other callers, responding only when he gets a new call from "S". They again spend hours together before going to a hotel room. Jonathan returns from getting ice to find that “S” is missing, with blood on the bedsheets. Someone knocks him out, and when he wakes up, the room is in order. He calls the police, but his story makes the detective think that he is delusional. Jonathan looks for Wyatt, but his law firm doesn't know him and a woman is living in what Jonathan thought was Wyatt's apartment.
Jonathan is surprised to find Wyatt waiting in his apartment. Wyatt is holding "S" somewhere, and will kill her unless Jonathan steals $20 million from an investment firm he will be auditing. He must wire transfer the funds, in Jonathan’s name, to a bank in Spain.
Jonathan receives a voice mail on Wyatt's cell phone from Tina, who seems to know Wyatt personally. Jonathan goes to her hotel room, where she reveals that Wyatt's real name is Jamie Getz, and that they met at a party hosted by the wealthy Rudolph Holloway. Jonathan researches Getz, learning that he is wanted for murdering Holloway.
At the audit, Jonathan executes the wire transfer. Wyatt texts a picture of "S" tied up in Jonathan's apartment, wishing them well. Just as he arrives at his apartment, Jonathan notices that the picture was taken before the pipe started leaking. He realizes that “S” is Wyatt’s accomplice – but his apartment suddenly explodes, witnessed by Wyatt from across the street.
Wyatt, travelling on a passport in Jonathan's name, meets "S" in a hotel in Madrid. She is upset that Jonathan is dead, but he reminds her that her $1 million share is more than she ever made as a prostitute on the street. When he attempts to withdraw the funds, he learns that the co-signer, Wyatt Bose, must be present. Wyatt exits the bank to find "S" gone and Jonathan waiting – the apartment superintendent died in the explosion, entering the suite just moments before Jonathan arrived. Jonathan has procured a passport using Wyatt's name. He demands half of the $20 million.
Leaving the bank, Jonathan offers Wyatt $5 million to tell him where "S" is. Wyatt agrees, then leads Jonathan to a quiet park and pulls a gun. Before he can shoot, Wyatt is shot by "S". Jonathan pursues her, leaving a dead Wyatt and all the money behind. She apologizes to him and leaves in a cab, in tears.
Jonathan stays in Madrid. One day, he and "S" spot each other across a plaza; they exchange smiles, and he goes to her.
Alternate Ending
Wyatt and Jonathan part ways with their shares of the money. Days later, Jonathan is walking around Madrid as he continues his futile search for "S."
