A USO girl defies the rules when she falls for a soldier visiting the star-studded Stage Door Canteen.

During World War II, soldiers "Dakota" Ed Smith, "California," "Tex" and "Jersey" ride a train bound for New York, where they will be shipped out. California, a naïve small-town boy, befriends Dakota, who has no family. When the soldiers arrive in New York, they are given twenty-four hours leave, and all end up at the Stage Door Canteen, a restaurant for servicemen operated by many famous personalities. Included in the Canteen's guidelines is the fact that female hostesses are not allowed to make dates with soldiers from the Canteen. The soldiers are surprised to meet comedian Ed Wynn checking hats, actor Alan Mowbray waiting tables and George Raft washing dishes. Aspiring actress Eileen volunteers as a hostess and meets Dakota, while her roommate Jean sits with California, and Ella Sue meets fellow Southerner Tex. Jersey, meanwhile, visits his fiancée Mamie in New Jersey. The next day, the soldiers are given more leave and Jersey gets permission from his commanding officer to marry Mamie, while the rest of the soldiers return to the Canteen. Although Dakota likes Eileen, he is put off by her snobbery and leaves. A battalion of Marines is ordered to ship out that night, and everyone joins in a chorus of "The Marines' Hymn" to show their support. Jean, delighted by California's sweet nature, agrees to be his "number one girl," and the next day at camp, Mamie arrives to marry Jersey. That same day, Eileen is thrilled when she gets a lead role in a play opposite Paul Muni, but her excitement is diminished by the realization that she genuinely loves Dakota, whom she has offended. That night at the Canteen, soldiers are entertained by Ethel Waters and the Count Basie Orchestra, and by a performance by renowned stripper Gypsy Rose Lee, among others. California sneaks in his first kiss ever with Jean. Despite regulations, Eileen and Dakota meet that night outside her apartment and become engaged. Because of this, Eileen is barred from the Canteen for breaking their rules. When actress Katharine Hepburn learns that the couple did not just date but became engaged, she bends the rules and allows Eileen in so that she can meet Dakota. Unfortunately, Dakota and his friends have all been shipped out, but an Australian soldier delivers a message from him that he wants to marry Eileen on his return. Hepburn gives the tearful Eileen a stern talk about supporting all the soldiers even though she misses Dakota, and Eileen returns to work in the Canteen.