Charlie McKenzie (Mike Myers) is a beat poet living in San Francisco, after having broken up with yet another girl based on paranoid perception. His policeman friend Tony tries to point out the pattern; that Charlie simply is afraid of commitment and tries to think of, or invent, any reason to break up with someone. Things pick up again when Charlie meets a butcher named Harriet and becomes infatuated instantly. After a while of driving near her workplace, he goes in and volunteers to help her out that day, and eventually a date ensues that evening, with him learning various factoids about her. He learns she used to live in Atlantic City, used to be involved with a trainer for Russian martial arts, and screams at someone named Ralph in her sleep. The next day she is gone when he awakes, but her sister Rose, whom she lives with, is there and tries to get to know him a bit. She then kindly warns him to be careful.Meanwhile, Tony begins losing his enthusiasm for his job on the police force, frustrated that there is no action or comparison to how they portray it on TV. He tries to get his chief to become shorter tempered, as per the stereotype in movies, by taking on bigger jobs. Charlie comes to Tony begging him to act as a voice of reason for the times ahead, not wanting to get hung up or paranoid about anything he may find odd about her.Charlie and Harriet begin falling deeper in love; he finds that she gets along great with his friends, they have perfectly matched passions, so he takes her to meet his parents. His parents Stuart and May are flagrantly Scottish, and tend to believe in conspiracy theories themselves, at which Charlie scoffs. His mother relies on the Weekly World News to keep her factually updated and keeps them stacked up as reading material. Charlie picks one up in the bathroom, out of bemusement, and finds an article on "Mrs. X", a bride who kills her husbands on their honeymoon, who seems to perfectly match Harriet. The killer's three reported victims were a plumber named Ralph, a lounge singer from Atlantic City, and a Russian martial arts student.Now strongly suspicious of her, Charlie begs Tony to investigate. After finding that the husbands in question that have disappeared have been reported missing along with their wives, Charlie tries to let the issue go. Unfortunately, his panic gets worse, suspecting her all the while but trying to cover it up, and eventually he breaks up with her.After a few days of gloom, Tony informs him that one of the husband's killers confessed. Charlie, realizing that he needs to make changes, rushes back to Harriet, informing her that he will see a therapist. He wins her over by playing one of his poems from her rooftop, and as they reconcile, every doubt he had gets disproved. Her friend Ralph was actually a girl, for example. At his parents 30th year anniversary, Charlie proposes to Harriet, and soon a wedding is underway. Later, they venture off to a secluded hotel up in the mountains for their honeymoon. Meanwhile, back at the police station, the chief informs Tony that the woman who had taken credit for the murder of the plumber was actually a compulsive confessor. Tony faxes a photo of Harriet to all of the known associates of the three missing husbands, and they all recognize her as their friends' wife.Tony tries desperately to contact Charlie but finds that the phone lines are down due to a storm where they are honeymooning, so he charters a plane. Upon landing he calls Charlie and warns him that Harriet is "Mrs. X", but before he can tell him anything else, their phone line gets knocked down, and the power goes out. Charlie desperately tries to escape, but Harriet finds him and begins acting unsettled and confrontational as he tries to leave her without letting on that he knows her traits. The endearing staff literally forces them into their hotel room to spend their first night together, and Charlie finds himself alone in the room with Harriet and an ax for the firewood.Harriet locks the door and begins telling him that she's been married before. He forces her into the closet and locks it, then looks down at their desk and sees a "Dear Jane" letter for Harriet, saying he has run away. Rose then leaps from the shadows and swipes at Charlie with the ax, stating that the husband "is never supposed to be in the room when the note is found", revealing herself to be the true killer. Charlie has no option but to run to the roof and try to evade Rose long enough for the police to show up. Eventually Tony leads the police into the hotel but arrests Harriet, still believing her to be the murderer. Rose swings the ax at Charlie and is thrown off the building, with only Charlie holding her up from falling to her death, prompting Tony to come to her aid.The authorities take her away, and Charlie and Harriet resume their lives afterward as a happy couple.