In London, newlywed Charles Sidley, suspecting that his American wife Belinda may be having an affair, goes to the Mayhew and Figgis Detective Agency to hire them to look into the matter. There, Charles, a staid accountant, tells Mayhew, the head of the agency, that Belinda has been coming home late at night and leaving early in the morning, leading him to conclude that she is seeing another man. Mayhew accepts the case and days later, when Charles enters his office, he comes upon a strange man dressed in a white raincoat and hat perusing the bookcases. After the garrulous man finally introduces himself as Julian Cristoforou, the detective assigned to Charles’ case, he unpacks a cache of macaroons, oranges and yogurt from his white messenger bag and begins eating. Prodded by Christoforou to disclose the details of his marriage, the reluctant Charles relates the first time he saw the waif-like Belinda: Spotting Belinda waitressing at a restaurant, Charles is intrigued and enters the establishment to have a meal. Amused when the charmingly incompetent Belinda dumps his food in his lap, Charles invites her out for dinner, and captivated by her enthusiasm and guilelessness, takes it upon himself to educate her about “culture.” Under Belinda’s influence, Charles begins to lose some of his stodginess, and flattered by her eagerness to absorb whatever he teaches her, he soon proposes and they are wed. In the present, Cristoforou queries what went wrong and Charles recounts how “his gay young pupil” became a “secretive little girl”: At a dinner party at their apartment attended by Charles’ business associates and conservative friends, Belinda listens to several of the guests touting a return to old-fashioned law enforcement principles such as public hangings and pillories. When she suggests that, following their reasoning, all rapists should be castrated, they react in horror, after which she sequesters herself in the bedroom. Exasperated, Charles tries to explain that marriage is a contract between two people expressing their obligations to each other, to which Belinda replies that obligations must be earned. Several days later, Charles is at a formal dinner party with his mother when Belinda fails to appear on time. They decide to start without her, and when Belinda arrives after everyone has finished eating, Charles simmers in fury. After the guests have departed, Belinda states that she was in the park watching dolphins and could not catch a return bus in time, but Charles accuses her of lying and having an affair. Back in the present, Charles insists that Cristoforou report his results from the ten days he spent following Belinda. Cristoforou dutifully recounts that Belinda visited the hat maker, ate ice cream at a coffee bar and spent six hours watching horror films. When Cristoforou mentions that he observed Belinda discreetly exchanging glances with an aristocratic man, Charles demands that he ascertain the name of that man. Later, when Charles chastises Belinda for arriving late to a concert, Belinda lambasts him for viewing marriage as a contract rather than a continuing courtship. When he then accuses her of having a lover, Belinda, shocked, tells Charles about her adventures: One day while taking a boat ride down the Thames to be alone, Belinda notices a strange man in a white raincoat watching her. Later, while walking down the street, she noticed the man on his scooter and since then has realized that he is following her. Soon, she begins to anticipate his arrival, and they take turns leading each other on various adventures. After Belinda concludes that although they have never spoken to each other, she feels alive when they are together, Charles realizes that she is talking about Cristoforou. Furious, Charles goes to Cristoforou’s apartment to confront him. Meanwhile, Belinda, finding Cristoforou’s business card that Charles has left next to their phone, proceeds to the address on the card and is shocked to find Charles with the man who has been following her. When Charles explains that he hired Cristoforou to follow her, Belinda declares that she never wants to see her husband again and storms out. Thirty-six hours later, concerned that Belinda is still missing, Cristoforou visits Charles and after announcing that he has resigned as a detective, offers to find Belinda, but warns Charles that she might not return to him. When Cristoforou finally locates Belinda, she berates him for making a fool out of her. Cristoforou counters that they spent ten joyous days together, during which she made him realize that anything was possible. After Belinda laments that she has only brought Charles misery, Cristoforou observes that she wants her husband back, but she says she only wants him forward, that is, if he once again becomes the man who courted her. Formulating a plan to reconcile the couple, Cristoforou phones Charles and instructs him to proceed immediately to his office. There Charles finds Belinda silently sitting in front of the bookcase. Cristoforou explains to Charles that Belinda will leave him forever unless he agrees to follow her for the next ten days. Once Belinda departs, Charles refuses to “play their game,” and Cristoforou admonishes that he must learn to love rather than dominate his wife. When Charles protests that he cannot leave his office for ten days, Cristoforou offers to take over for him, answers his phone and introduces himself as Charles’ “new partner.” Handing Charles his white raincoat, Cristoforou urges him to go to Belinda. On the sidewalk below, Charles spots Belinda and she turns to smile at him as she leads him through the London streets.