Historian Bettany Hughes retraces the lives of three great thinkers whose ideas shaped the modern world - Karl Marx, Frederick Nietzsche and Sigmund Freud.

Bettany Hughes travels to Vienna on the trail of Sigmund Freud, the father of psychoanalysis. Freud's influence surrounds us. In our vocabulary - repression, penis envy, the Freudian slip - and in the freedom we take for granted, to talk openly about our deepest feelings and insecurities