Contrary to popular belief, the Nelson Eddy-Jeanette MacDonald Technicolor confection Sweethearts is not based on the 1913 Victor Herbert operetta of the same name (though most of Herbert's songs remain intact), but a Dorothy Parker-Alan Campbell brainstorm about a popular Broadway singing duo, starring in a long-running production of Sweethearts. The early portions of the film take place during a purported presentation of the Herbert piece, with Eddy and MacDonald singing their hearts out and Ray Bolger providing comic relief. We then segue into a long sequence wherein producer Frank Morgan, celebrating Sweethearts's six-year run, insists that Eddy and MacDonald attend a lavish party, where the weary performers are called upon to continue singing throughout the evening. Hoping for a few moments alone after escaping the party, Eddy and MacDonald are besieged at their apartment by friends, co-workers, hangers-on and sponging relatives. Seeking peace and quiet, the couple agrees to leave Sweethearts for the comparative calm of Hollywood. But their entourage, fearing that they'll lose their meal ticket if Eddy and MacDonald leave New York, arrange to inaugurate two profitable road companies of Sweethearts by contriving to split up the loving couple. Cleverly sidestepping the sugary sweet sentimentality that one might expect from an MGM musical of the era, the delightful Sweethearts is hampered only by its overlength.