Piano teacher Polly Jasper is in the middle of a lesson when music publishers Joe Lathim and Dave Clark burst into her office and ask her to recommend a pianist. Polly is won over by their glib talk and agrees to become their new song plugger. Unknown to Polly, Lathim and Clark are on the verge of bankruptcy and lost their previous song plugger because they could not pay his wages. One afternoon, cowboy Jeff Williker comes to the office, and Polly is impressed with his composition, a pleasant song called "Kansas City Kitty." Using a check from a bank in which they do not have an account, Lathim and Clark get money from the building superintendent, and buy the rights to Williker's song. The song quickly becomes a hit, and Polly spends her time filling orders for sheet music, pushing the song at nightclubs and pining over dentist Henry Talbot, with whom she is in love. Henry, who is working on an encyclopedia of American popular music and its origins, is oblivious to Polly's romantic intentions, and continually turns down her dinner invitations. Back at the office, the building superintendent becomes infuriated when Lathim and Clark's check bounces. They attempt to pay him out of earnings from "Kansas City Kitty," but are horrified to discover that their bank accounts are frozen because of a pending lawsuit. Oscar Lee, an unknown songwriter, is suing them for plagiarizing his song, "Minnesota Minnie." Desperate to leave before the superintendent has them jailed and Oscar catches up to them, Lathim and Clark convince Polly to buy the business. Not having enough money of her own, Polly borrows a substantial sum from her roommate, Eileen Hasbrook, even though Eileen and her fiancé, band leader Jimmy, were saving the money to buy furniture. Jimmy is happy about their purchase, however, when he learns that it includes the rights to "Kansas City Kitty." Feeling confident that they have proven to Jimmy that women can make smart business decisions, Polly and Eileen are devastated to learn about the lawsuit. Determined to get Oscar to drop the suit, Polly invites him to dinner, where she attempts to romance him. Unfortunately, it is the same night that Henry finally decides to accept Polly's standing dinner invitation, and Polly winds up eating two dinners, one with Oscar in the dining room, and another with Henry in the bedroom. Polly succeeds in getting Oscar to propose, but chaos reigns when Jimmy sees Oscar holding Eileen and teaching her to blow smoke rings, and Oscar then catches Polly with Henry. Oscar storms out, and soon Polly faces him in court. During the trial, Polly plays several classical melodies for the judge, and shows him how they have been used for popular songs. The judge agrees that it is possible for the same thing to have occurred with Oscar's and Jeff's songs, but will not let Polly use the theory as a defense unless she can identify the older tune on which "Kansas City Kitty" is based. Just then, Henry arrives and produces an old music box to prove that both Oscar and Jeff based their songs on a 140-year-old melody. The case is dismissed, but before Polly can leave, the starstruck judge plays his version of the song, "California Carrie."