The title of this episode refers to the Arlen-Harburg song from the 1939 film The Wizard of Oz. As the war breaks out, cinemas are closed in London, leading kitchen maid Eunice to wonder whether she'll ever see that film. Apparently, the song was already quite popular in Britain before the film was released.
Hallam: (explaining the wedding in the servants quarters) I'm sure the normal scheme of things will resume this evening.
George, Duke of Kent: There is no more normal scheme of things. As long as this war lasts, we're each other's servants.