Tonight Mastermind celebrates its 250th edition. During the last 15 years nearly 1,000 contenders have sat in the famous black chair 5 to be asked around 36,000 questions. Four more contenders now seek a place in this year's semi-finals in the Gulbenkian Theatre at the University of Kent, Canterbury. Donald MacCarron (publicity executive) The history of powered flight since the Wright brothers Michael O'Sullivan (local government officer) The lives and works of the Strauss family, 1825-1940 Peter Chitty (telephonist) History of the British Secret Service, 1909-1940 Margaret Spiller (civil servant) The life and times of Emperor Nero, AD37-68