Bettany begins her journey in the city of Trier on the banks of the Mosel in Germany. It was here on the 5 May 1818 that Karl Marx, one of the most important philosophers of the 20th century was born.

Bettany searches to clarify the beliefs of a man whose work is possibly the most devastatingly manipulated and misinterpreted in philosophical history. The 19th century philosopher, Friedrich Nietzsche was one of the most brilliant and dangerous minds of the century.

Freud's influence is all around us. In our vocabulary - repression, penis envy, the Freudian slip - and in the freedom to talk openly about our deepest feelings and insecurities. But what do you learn when you take a Freudian approach to Freud himself? Historian Bettany Hughes travels to Vienna to discover how his childhood experiences led to the formation of the father of psychoanalysis.