Overview: The second semi-final of the Mastermind series comes from Blackpool Tower Circus. In the spotlight are Church of England parish priest Richard Sturch, from Kidlington in Oxfordshire; mature student Russell Turner, from Hethersett in Norwich; senior library assistant Robert Devlin, from Belfast; and political risk consultant Boris Starling, from London. Their specialised subjects are Emperor Frederick III, anarchism 1840-1939, 19th-century Irish history and Dick Francis and his novels. Magnus Magnusson asks the questions.