Switchboard operator Ella Peterson works for telephone answering service Susanswerphone in owner Sue's Brooklyn Heights basement apartment. Despite Sue's orders strictly to "take and give" messages, Ella uses a variety of character voices to generously assist subscribers in their professional and personal life, including even posing as Santa Claus to help a mother convince her child to behave. Ella is especially concerned about playwright Jeffrey Moss, with whom she calls herself "Mom" because, she insists, the sensitive man has recently lost his writing partner and needs motherly reassurance. Ella's shy and clumsy behavior and her secret crush on Jeffrey prevent her from any real romance. One day, when Jeffrey confides in "Mom" that his producer Larry Hastings has given him one day to finish the outline for his new play, "Midas Touch," "Mom" tries to boost his ego, but Jeffrey soon loses his self-confidence and drinks himself to sleep. Meanwhile, Inspector Barnes and his assistant Francis, who suspect that Susanswerphone is actually a prostitution ring, pose as magazine reporters and interview Ella while surreptitiously wire-taping the switchboard in hopes that an arrest will lead to Barnes’ immediate promotion. When opera singer “Mme.” Grimaldi calls, Barnes believes she is the “madame” of the prostitution ring and warns Sue and Ella he is putting them under surveillance. Soon after, Sue's boyfriend, a debonair European named J. Otto Prantz, moves into the apartment to run his music distribution business, Titanic Records, which is actually a front for a bookkeeping operation. During a secret meeting with his bookies, Otto explains the new system: When customers place their bets, the specifics will be translated into a classical music record album code in which, for instance, “Beethoven” is actually Belmont Park and “five hundred orders” is a $500 bet. The next morning, when Jeffrey does not answer Ella's wakeup call, she goes to his apartment and awakens him, excited finally to know what he looks like. Claiming to have the wrong address, Ella introduces herself as "Melisande Scott." When Jeffrey flirts with her, Ella insists that he is just trying to avoid writing and then reminds him that he has written without a partner before. Jeffrey thinks that her intuition about his past behavior is "uncanny" and begins to work, inspired by her confidence in his ability. After Larry approves the outline, Jeffrey asks Ella for her number, but she refuses and instead sets a date to meet at his apartment the following week. Days later, Ella discovers the Pyramid Club is holding auditions for song writers and, despite Sue's orders otherwise, makes an appointment with subscriber Joe Kitchell, a dentist who longs to become a professional song writer. When Kitchell asks her to give him a subject to test his lyrical ability, Ella blurts out "midas touch." After Kitchell sings a ditty using his air hose as a microphone, Ella gives him the Pyramid Club advertisement, then disappears. Meanwhile, Francis, secretly photographs the transaction. Days later, when Ella learns from Larry's messages that subscriber Blake Barton's casual manner and sloppy appearance have lost him the audition for a part in Jeffrey's play, Ella , dressed as a beatnik, visits Barton at his café hangout and suggests that he wear a suit and repeat the audition. Once again, Francis is lurking in the shadows and takes a picture. Later at the office, Ella is taking Titanic Record orders, when neighbor Carl, an avid classical music fan, notes that an order for Beethoven's tenth symphony must be wrong, since the composer only wrote nine, prompting Ella to change several large "shipping" orders. In a moment alone with fellow operator Gwynne, Ella despairs that she has lied to Jeffrey about her real identity. When he calls moments later to ask "Mom" if there are any messages from "Melisande," Ella hears actress Olga in the background trying to seduce Jeffrey. Jealousy finally prompts Ella to race to Jeffrey's apartment, where she announces she is Jeffrey's secretary and pushes Olga out the door. However, she is too shy to admit her crush or her real identity and attempts to leave, but when Jeffrey professes his love, Ella collapses into his arms and kisses him. Once again, Francis, hiding on the balcony, takes a photograph. One evening, after Jeffrey sings to Ella about the timeliness of her arrival in his life, a nervous Ella reluctantly agrees to go to a star-studded party. Noticing that the crowd's conversations are filled with name-dropping, Ella attempts her own version but only comes up with dog stars "Rin Tin Tin" and "Lassie." Just as Ella decides she must tell Jeffrey the truth, a butler delivers a note from Jeffrey asking her to marry him. Ella replies with "Goodbye" and leaves the party. While walking home, she laments that Jeffrey is in love with "Melisande," not her. Meanwhile, when two gangster mugs threaten to kill Otto for lost "Beethoven" bets, he deludes Sue into investing her capital into his "business" and uses the money for the payoff. Unable to find "Melisande," Jeffrey spends that night drinking at the Pyramid Club, where Barton introduces himself as the new actor in Jeffrey's play and tells him the story of the "miracle" girl who gave him audition advice. Suddenly, the stage show begins as a chorus line of dancers sing "The Midas Touch." Struck by the coincidence, Jeffrey approaches Kitchell, who tells the story of his "miracle" girl who gave him the idea for the song. Later, when Jeffrey discovers the men are also Susanwerphone subscribers, he realizes "Mom" is the miracle girl. At Susanswerphone, Ella is tired of living through others' lives and vows to return to her old job at a brassiere company switchboard. As she packs to leave, the mugs arrive for their money. When Ella explains to Otto that she "corrected" his orders, Otto, in frustration, blurts out that she put the wrong bookings on the wrong horse. Desperate to help Sue retrieve her life-savings, Ella warns the mugs that they have been taperecorded by the police. When Barnes arrives a few minutes later to arrest Ella and Sue, Ella loudly announces that Otto is running a large-scale booking operation under the Titanic Record front. Mindful of his promotion, Barnes arrests Otto and the mugs and admits he misjudged Ella. When Jeffrey arrives soon after, Ella tries to disguise herself as "Mom" using an afghan, eye glasses and a mop head, but Jeffrey sees through her disguise and asks Ella that she give her love solely to him, instead of "scattering it" to all the subscribers. After Larry, Kitchell, Francis, Gwynne, Barton, Sue and others congratulate the couple, Ella and Jeffrey dance out into the night while Susanwerphone's bells keep ringing.