It's Vienna, 1909 and the double murder of an arms dealer in police custody and a senior public official has shaken Vienna to its core. Doctor Max Liebermann has only just returned from a lecture tour when Inspector Rheinhardt asks for help in what could be the most dangerous case of their career.

Oskar and Max discover a conspiracy that leads to the heart of government. Can the Freudian psychoanalyst and the detective do enough to stop a seditious mole known as 'Mephisto' from bringing the Austro-Hungarian Empire to destruction? And will their lives ever be the same again?