Irish Luck: Tom Donahue, a New York traffic cop, wins a trip to Europe in a newspaper contest, and he decides to visit relatives in Ireland. Arriving in Dublin, he learns that he is an exact double for Lord Fitzhugh, a young Irish aristocrat with whom he becomes friends. The Earl of Killarney, Fitzhugh's uncle, who is on his deathbed, wishes to see his favorite nephew and wipe out past animosities. Fitzhugh, in the meantime, has disappeared, and his sister, Lady Gwendolyn, persuades Tom to take his place.