Timid accountant Jonathan McQuarry (Ewan McGregor) is an auditor with little to no social life. One night while working late in a boardroom he is interrupted by a lawyer, Wyatt Bose (Hugh Jackman), who befriends him and offers him marijuana. After a long conversation, Jonathan takes the subway home where he has a brief encounter with a blond woman (Michelle Williams) with whom he falls in love at first sight while waiting for the train. Upon returning home he notices a pipe in his bedroom is leaking and leaving a stain.Jonathan contacts Wyatt the next day and they play tennis after work. Afterward they stop by Wyatt's lavish apartment where Jonathan borrows an expensive suit, and they go out to a club. They meet again for lunch the next day where Wyatt mentions he is leaving on a business trip to London for a few weeks. Upon leaving, Wyatt unintentionally takes Jonathan's mobile phone instead of his own.When Jonathan realizes the phones have been switched, he attempts to contact Wyatt but does not reach him. He is soon contacted by a woman (Natasha Henstridge) who asks if he is free that night. He informs her that he is and agrees to meet her. When she arrives they proceed directly to a hotel room to have sex and Jonathan realizes that Wyatt must be on some type of exclusive list.When Wyatt calls the next day, he doesn't mind Jonathan using the list and even encourages him to continue. Jonathan initiates his first call and has an encounter with an attractive older woman (Charlotte Rampling) who explains how the list works. The list consists of business men and women, too busy to have any real social life and looking to have casual sex once in a while. She also explains the list's rules: the initiator pays for the room, no names are exchanged, no business talk, very little conversation and no rough play. Jonathan later spots the older woman on the cover of Forbes and smiles. Over the next few weeks he engages in sexual encounters with several other members.One night after initiating another encounter, Jonathan is surprised to find that his partner is the blond woman he met while waiting for the train. When she begins to undress he stops her and tells her that they have met once before. He requests that she have dinner with him and they order room service and talk for hours. Even though Jonathan ask many times, she never reveals her name. The next day Jonathan rejects other callers from the list but when the blond woman calls again they agree to meet for dinner in Chinatown. They then proceed to a hotel where she requests some ice. When Jonathan returns to the room she is gone and there is blood on the bedsheets. Someone knocks him out from behind and when he wakes up the bed has been made. He contacts the police and explains to Detective Russo (Lisa Gay Hamilton) that the woman is missing but realizes he has little to no information about her. The detective challenges his story thinking he is delusional. Jonathan tries to trace Wyatt but soon realizes that the Wyatt he knows doesn't exist when nobody seems to know him at work or in his apartment building.Upon returning home Jonathan is surprised to find Wyatt waiting for him and claiming he's holding the blond woman captive. He makes a deal that he will leave the blond woman unharmed if Jonathan agrees to steal millions of dollars from a corporation he is scheduled to audit in a few days. Jonathan reluctantly agrees.The following night at work, Jonathan receives a call asking if he is free. The woman calling happens to be Tina (Maggie Q), the woman who introduced Wyatt to the sex club list. She reveals that Wyatt's real name is Jamie Getz, and that they met when he was attending a private corporate event as a guest of Rudolph Holloway, an investment banker with whom Getz played tennis. Jonathan finds out through research that Getz murdered Holloway, strangling him with tennis strings, and also served three years in prison for insurance fraud and arson. Jonathan is later notified by the detective that a blond woman matching his earlier description was discovered dead. When he comes in to identify her, he sees that it is actually the first woman who called him, and that she was also strangled by tennis strings. When Jonathan returns home, he notices his own tennis racket is missing and realizes he could be framed for murder.Back at work, he completes a wire transfer to a bank in Europe in his name like Wyatt asked. As soon as the transfer is confirmed, Wyatt sends a picture of the blond woman still captive but in Jonathan's apartment. On his way home he notices that the picture Wyatt sent him was taken in his apartment before the pipe started leaking; there are no stains on the wall. Jonathan realizes that she has been working with Wyatt all along and that everything since meeting Wyatt has been planned. He wisely avoids his apartment which explodes when the superintendent enters to fix the pipe. Detective Russo arrives and believes Jonathan to be dead.Later, Wyatt impersonates Jonathan and attempts to withdraw the funds from the bank but is denied access because his cosigner is missing. Wyatt realizes Jonathan added a cosigner to the account to screw him out of the money. He leaves angry thinking he's gonna have to find a partner to impersonate the cosigner. He is surprised when Jonathan shows up and offers to help him withdraw the funds with the condition that he gets half. Wyatt agrees and the transaction is completed.Outside the bank, Wyatt attempts to shoot Jonathan but before he is able to do so he is shot by the blond woman who quickly leaves. Jonathan leaves the money behind to pursue her and asks her to talk to him but the girl tells him that she wants to call it off and apologizes to him as she didn't know Wyatt was planning to kill him. The girl gets into a cab and leaves as Jonathan watches her go.Later in Spain, Jonathan again crosses paths with the blond woman and they exchange smiles. The movie comes to a close as Jonathan walks to her and she stands waiting for him.