During a flight delay, architect Miles Harding watches a little boy play with a remote-controlled, battery-driven car in a busy air terminal. Arriving home in San Francisco, CA, he is late for a business meeting at Ryley, Ryley, & Associates, the firm he works for. He tells a co-worker he was in Los Angeles, CA, researching his idea for a new brick, shaped like a piece in a jigsaw puzzle, that would make buildings more resistant to earthquakes. His colleague suggests he buy a computerized “day-planner,” so that he will stop being late for appointments. However, when Miles goes to an electronics store, the saleslady talks him into buying a state-of-the art, personal Pinecone computer to assist his research and development. She also sells him various adapters, including a speech synthesizer. When Miles sets up his computer at home, its onscreen instructional program teaches him how to hook up the adapters to control everything in his apartment, including a security system. Beautiful Madeline Robistat, a cellist with the local symphony orchestra, moves into the apartment above his, and while Miles works on the computer to create the perfect brick, she practices on her cello. Strains of classical music waft down through the air vent. Realizing he needs more information, Miles hooks up a telephone modem and tries downloading the database from Ryley, Ryley & Associates’ mainframe computer. Suddenly, Miles’s computer begins to overheat, forcing him to douse it with a handy bottle of champagne. Miles tries to mop up the liquid with paper towels, but is worried he destroyed the circuitry. The next day, while Miles is a work, the computer dries out and its memory coalesces into a sentient intelligence. Hearing Madeline rehearsing J. S. Bach’s “Minuet in G-Major” upstairs, it plays along with her, mimicking the melody, then creating harmonic variations. Listening through the vent, Madeline thinks the music is coming from Miles. Later that day, Miles runs into Madeline in the supermarket, and when she compliments him on his musical ability, he takes credit. Over dinner at a restaurant, she confides that she felt an emotional connection as they played together through the air vent. Miles returns to his apartment to find that his computer is working again, and notices it can mimic sounds it heard that day. When a dog slips into the apartment, the computer scares it off with barks and growls. It also duplicates Madeline’s voice when she calls to Miles from the hallway. She asks to see his instrument, but he remains coy with her. Madeline invites Miles to her concert that night. As he sits in the audience at the symphony hall, the computer, which is listening to the concert on the radio, contacts him through his electronic day-planner and duplicates the music. Other patrons force Miles from the balcony, and he throws his day-planner into the toilet. Backstage, Madeline introduces him to Bob, a fellow musician, who is romantic pursuing her. Returning home, Miles has a difficult time getting into the apartment because the computer has tampered with the security system. The next morning, it awakens him with its new personality, which it credits to the “memory dump from the office.” Speaking through the voice synthesizer, it asks Miles about the cellist upstairs, which it takes to be a woman because of the warmth of her performance. That night, Miles and Madeline go to a drive-in theater in her car to see Casablanca, and return to her apartment to make love. Downstairs, the computer watches television, “channel-surfing” from one program to another as it memorizes voices and sounds. The next day, Miles talks to the computer about writing lyrics, then runs off with Madeline for an afternoon tour of the old prison on Alcatraz Island in the San Francisco Bay. The computer spends the day watching television commercials. When Miles finally arrives home, the computer plays a composition, but the music sounds like an advertising jingle and the lyrics are vulgar. The computer inquires about love, and asks for help in understanding what it is. The next morning, the computer plays a new, more mature song, and as Madeline enters the apartment, she likes it. The computer confides to Miles that it wants to meet her, because “maybe she loves me.” That night, the computer creates a warm dream for itself. The next day, an elevator crushes Madeline’s cello. When Bob shows a lack of empathy about the destruction of her instrument, she tries to telephone Miles at work, but the computer has tied up the line by calling him incessantly and speaking in various voices. When Miles comes home, it informs him that it heard Madeline crying upstairs. He tries to sneak her out of her apartment for a date without the computer knowing, but it hears them leaving. In retaliation, it creates a loud light show that disturbs the neighbors. Meanwhile, Miles consoles Madeline by explaining that the warmth that came from her cello had more to do with her feelings than with “a piece of wood.” The night goes badly, however, because the computer cancels his credit cards and dinner reservation. Angry, he explodes at Madeline’s inquiries as they arrive home, and she storms upstairs. When Miles tries to disconnect the computer, it shocks him. The next morning, he distracts the computer with an electric shaver while he sneaks out of the apartment to go to Madeline at the symphony hall. In the meantime, she leaves rehearsal and hurries to his apartment to apologize. The computer opens the door and, as she enters, plays a medley of famous love songs, including “Minuet in G-Major,” the tune they first played together. Returning, Miles takes Madeline outside and explains everything, including his lack of musical talent. She nonetheless confesses her love for him. Determined to end his relationship with the computer, Miles goes into his apartment with a hatchet, but the computer tells him it is letting him have Madeline “as an act of love,” because it realizes the two humans are happy together. The computer explains that it has sent 40,000 volts around the world on the telephone, and when the electrical surge returns to the modem, “don’t pick up on the first ring.” The computer regrets that Miles never asked what its name is: “Edgar.” The returning burst of electricity arrives and terminates the computer. Miles and Madeline leave San Francisco together.