Daniel Francis O'Toole, singing maestro in a New York restaurant, finds himself the unexpected heir to an estate in Ireland. He doesn't have money enough for the passage to Ireland, but the band members decide to incorporate him, advancing him the fare for equal shares in the estate. In Ireland, Danny finds that his is only a half-share, and the other half belongs to Mavourneen Kerrigan and she has the exclusive right to sell or keep the property...which, despite his pleas, she refuses to do. She also declares him an undesired guest, objects to his presence and insists that he prepare his own meals. He does so in a large main hall, but can only make hamburgers. During a rainstorm, Dorothy Stonewall and her parents, seek shelter in the castle, meet Danny there, and are invited to dine with him...on hamburgers. They find hamburgers to be a delicious novelty, and the inspired Danny establishes Ireland's first fast-food operation (in a castle, at least), and soon he has a thriving operation . His band members from New York show up, and provide music for the customers while Danny Sings---and there is no doubt that this IS Ireland's first castle-housed fast-food operation providing live music and hamburgers. Mavouneen has taken a liking to Danny, but gets jealous when she thinks he is paying too much attention to Dorothy and decides to sell the castle, and this is not good news to the band members who are doing a thriving business selling white-castle hamburgers. So they contrive to reunite Danny and Mavourneen.