They were playing "The Categorical Imperative" that evening at the Little Theatre in Unter den Linden. It is an old-fashioned comedy laid in the Vienna of 1815 - two love-stories, lightly and quaintly told, across which, through the chatter of a little Viennese salon, we dimly see Napoleon return from Elba and hear the thunder of Waterloo. A young cub of a Saxon schoolmaster, full of simple-hearted enthusiasm and philosophy, comes down to the Austrian capital, and, taken up by a kindly, coquettish young countess, becomes the tutor of her cousin, a girl as simple as he.