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

Born in the 19th century, they lived through a time when old certainties were breaking down. Regimes were overthrown by mass uprisings, science was undermining religious authority. Their challenge was to figure out what makes us human in a fast-evolving world.