A bump on the head sends Hank Martin, 1912 mechanic, to Arthurian Britain, 528 A.D., where he is befriended by Sir Sagramore le Desirous and gains power by judicious use of technology. He and Alisande, the King's niece, fall in love at first sight, which draws unwelcome attention from her fiancée Sir Lancelot; but worse trouble befalls when Hank meddles in the kingdom's politics.

Small-time businessman Charles Engle is threatened with exposure for embezzling $3,000 for his free-spending wife. Deciding on suicide, he scribbles a note, stuffs it in his pocket and goes for one last night on the town. He is pulled into a poker game by conman Bill O'Brien and singer Nina Barone, but when they discover the dropped note, they resolve to turn the tables, get Engle his $3,000 and save his life.

In 1911, minor stage comic, Vernon Castle meets the stage-struck Irene Foote. A few misadventures later, they marry and then abandon comedy to attempt a dancing career together. While they're performing in Paris, an agent sees them rehearse and starts them on their brilliant career as the world's foremost ballroom dancers. However, at the height of their fame, World War I begins.