Jerry Green, an aspiring children’s book author, recites story ideas into a hand held tape recorder as he commutes to his job at Macy’s department store in New York City. At work, Jerry spots Jenny Moore walking through the store with her toddler son, Benjamin. Instantly smitten, Jerry rushes over and helps Jenny when she drops her bags, then invites her to lunch. In the park, Jerry tells Jenny about his work, but he notices her wedding ring and is disappointed she is not single. That evening, Jerry goes to dinner with Helene, a co-worker he casually dates. When Helene brings up marriage, Jerry balks. He ignores her when Jenny arrives at the restaurant with her husband, Preston Moore. Annoyed, Helene leaves. Meanwhile, a bored Jenny listens to Preston brag about his insurance job then leaves the restaurant without him. Jerry follows Jenny outside and they go for a walk, where Jerry inquires if she is in an unhappy marriage. When she says yes, he kissers her, but Jenny’s neighbor, Ernest Van Santen, jogs by and says hello and Jerry worries that he will tell Preston. When Jenny seems unconcerned, Jerry blurts out “I love you!” Flattered, Jenny asks Jerry out on a date. The next evening, Jenny takes Jerry back to her apartment and confesses she has a loveless marriage. Proclaiming their love for each other, Jerry and Jenny kiss and Jerry notices neighbors watching through the window. When Preston returns home, Jerry and Jenny hide upstairs but hear Preston talking with another man downstairs. When the man leaves, they go downstairs to find Preston dead, stabbed in the back. Stunned, Jenny wants to call the police but Jerry points out that they appear suspicious, as two lovers caught by a jealous husband. When Jerry has Jenny call Martin, the night doorman, to ask if a man came in with Preston, they learn that Preston came in alone. Jerry convinces his lover they need to investigate the murder to clear their names and stuffs Preston’s body in the kitchen freezer. The next day, Jenny calls Preston’s secretary, Herbert Little, and lies that Preston is home sick with the flu. Jerry babysits Benjamin while Jenny goes to Preston’s office and retrieves his appointment diary and briefcase. Back at the apartment, Frank Danzinger knocks on the door, identifying himself as a police detective and claiming there have been multiple break-ins in the building recently. Danzinger looks around the apartment. Jerry nervously follows and Benjamin crawls under the dining room table. After Danzinger leaves, Jerry retrieves Benjamin and finds a recording device under the table. When Jerry meets Jenny in the park, the lovers run into neighbors Ernest and his wife, Audrey, who insist Jerry and Jenny join them for a drink at their place. At the Van Santen’s apartment, Jerry excuses himself to the bathroom and discovers another tape recorder. He plays it back and hears a conversation he and Jenny had earlier, then insists they leave. Later, Jerry informs Jenny that the Van Santens are wire-tapping her apartment. As Jerry goes through Preston’s files, he questions if Jenny ever met Danzinger, but she does not remember him. Thinking the Van Santens have gone out for the evening, Jerry breaks into their place to steal the tape recordings but finds the couple stabbed to death. He runs to the bathroom and vomits in the toilet; upon flushing it, he hears a strange clanking noise. Checking the tank, Jerry finds a bag of expensive jewelry. Jerry takes Jenny and Benjamin to his apartment. As Benjamin sleeps, Jerry finds a file that insures the jewelry he found for $1.5 million. Jenny remembers Preston telling her his company had an illicit policy, where clients would claim their property was stolen to collect on its insurance, only to have the items returned with a fifty percent cut of the proceeds going to the insurance company. Jerry thinks Preston, the Van Santens and Danzinger were sharing the insurance company’s profits and Danzinger killed the others. The next day, Jerry hides the jewelry then returns to Jenny’s building in disguise. He plants a ransom note for the jewelry in Jenny’s apartment then climbs into the Van Santens’ apartment to do the same, but is shocked to find Danzinger inside, stabbed to death. As Jerry runs out, a mysterious man picks up the note, which instructs the reader to wear a beret and meet Jerry at Macy’s that afternoon. While at work, Jerry phones Jenny to tell her about Danzinger. Jenny think it is time to call the police but Jerry refuses because he has not yet proven his innocence by implicating the real killer. After she hangs up, Jenny leaves Jerry’s apartment with Benjamin. Meanwhile, Jerry leaves notes all over the city with the intent of luring the killer to the police. At Macy’s, Jerry sees a French man with a beret and sends Helene over with a second note as Preston’s secretary, Herbert, watches from afar. After trying to call Jenny back all afternoon, Jerry is relieved when she shows up at Macy’s after sending Benjamin to her maid’s house. Jerry tells Jenny of his plans to lure the killer to the police with his notes but Herbert eavesdrops and lies in wait until the store closes. After killing a security guard, Herbert corners the lovers as Jerry surreptitiously turns on the tape recorder in his pocket, documenting Herbert’s demand for the jewelry, confession to all of the murders, and to the insurance scheme. Jerry tackles Herbert and disarms him long enough for he and Jenny to escape. They run to the store’s basement, where Herbert chases them through a maze of giant toys, but they eventually overpower Herbert and knock him unconscious. Jerry pulls out his tape recorder, confirming that he captured Herbert’s confession and the couple goes to the police.