In East Los Angeles in the 1920s, Alton Glenn Miller fends off poverty by repeatedly hocking his trombone from pawnshop owner W. Kranz and then buying it back when he earns a little money. While attending yet another musician-for-hire job with his best friend, pianist Chummy MacGregor, Glenn is thrown out yet again for playing his jazzy arrangements. Soon after, Kranz informs them that Ben Pollack is holding tryouts for his band the next week. Hoping to sell his arrangements, Glenn leaves his trombone and brings only his work to Ben, who spurns them. After Chummy slips them to an auditioning musician, however, Ben hires Glenn immediately. With his advance, Glenn buys faux pearls for his college sweetheart, Helen Burger, but when the band tours near her Denver, Colorado home a few weeks later, Helen, who has not heard from Glenn in two years, barely remembers him. Undaunted, Glenn insists that she meet him after his job that evening, but by midnight, Glenn has not appeared and a furious Helen goes to sleep. Three hours later, Glenn wakes her outside her window, quickly charming her into driving to his parents' house nearby. At the Millers', Helen is surprised to discover that the whole family considers her Glenn's girl friend. They then visit their alma mater, the University of Colorado, where, to Glenn's chagrin, Helen admits that her favorite song is "Little Brown Jug." Although Helen begins to fall for his sincerity and passion for creating a new style of music, Glenn races off to join Chummy, promising only to call from the road. Two years later, Ben's band is gaining in popularity and moving from New York to Atlantic City, but Glenn remains behind, hoping to work on his arrangements with the help of band booker Don Haynes. Soon, Glenn is back to pawning his trombone, and accepts an offer to play in an orchestra for a musical play. One night, upon hearing "Little Brown Jug," Glenn calls Helen and asks her to come to New York that night to get married. Although she responds that she is engaged to another man, Glenn, ignoring her protests, urges her to call the number Pennsylvania 6-5000 when she arrives. Helen is at first disdainful, but, drawn to Glenn, soon finds herself on a train to New York. There, Glenn sweeps her over to their impromptu wedding service, and that night after Glenn's show, the couple return to their honeymoon suite to discover that the boys in the band have arranged a night out at Connie's Inn in Harlem. At the club, Glenn joins jazz greats such as Louis Armstrong and Gene Krupa onstage, finally carrying Helen over the threshold around dawn. Months later, Glenn is working steadily as a musician, but Helen prompts him to return to his dream of arranging. With her encouragement, he begins studying new compositions and writes "Moonlight Serenade." They are dismayed, however, when the song is converted into a nightclub number, and Helen convinces Glenn that he should form his own band. He, Chummy and Don put together a budget that seems unattainable, but Helen calmly reveals that she has been saving for the "Glenn Miller Band Fund" for years. Six months later, the band is barely breaking even, and Glenn despairs that he may never find the special sound for which he is searching. When their truck breaks just before a job at Boston's State Ballroom, Glenn stays behind, and later discovers that it has been cancelled and Helen is in the hospital, having collapsed from an exhaustion-induced miscarriage. Although the doctor declares that Helen can no longer bear children, Glenn promises that they will have a boy and a girl. The next day, State Ballroom owner Si Schribman visits Helen and, sorry for having cancelled the band, agrees to book them for an upcoming date. Glenn insists upon hiring a large band, and with Si's backing, tries out new arrangements. The night before they open, the trumpeter cuts his lip, and when Glenn replaces him with the clarinetist on "Moonlight Serenade," he finally achieves his unique sound, and a standing ovation. Over the next years, Glenn's sound sweeps the country, propelling his records to the top of the charts and providing Glenn, Helen and their adopted son Stevie with a luxuriant life style. On the couple's tenth anniversary, Glenn and Helen each plan a surprise for the other: Helen introduces Glenn to his new adopted daughter, and he throws her a party at which he plays his new song, "Pennsylvania 6-5000," and presents her with a small brown jug as a gift. Later, as Glenn scores a Hollywood film, Helen delivers the War Office letter which designates Glenn as an Army captain, and supports his decision to travel overseas to play for the troops. At first, Glenn is forced to lead the Army band in dull marching tunes, but when he spices up the marches, an impressed Gen. Arnold promotes him to bandleader. Assigned to London, Glenn bids his family a tearful goodbye at the airport, promising to "be right back." Overseas, the soldiers cheer as Glenn bravely leads the band amid air raids and falling bombs. While the war rages, through the invasion of France, D-day and the Allied liberation of Paris, Glenn writes to Helen about his postwar plans, and urges her to listen to his Christmas broadcast from Paris. On 15 Dec. 1944, he boards the flight from London to Paris, but the plane never lands. Just before Christmas, Helen receives the news that Glenn has disappeared, and, though devastated, listens to the Parisian broadcast with the children, Chummy and Si. When she hears Glenn's band playing his newest jazz arrangement of "Little Brown Jug," Helen realizes that Glenn's music and legacy will remain long after his death.