The semi-final stage of this year's competition is reached tonight in the Great Hall of the University of Lancaster. Four winners of the first-round programmes compete for a place in the final of Mastermind 1985.Sharon Colesell (invoice clerk) The Decameron of BoccaccioClive Bettington (solicitor) The Second Anglo-Boer War 1899-1902Catherine Walling (assistant museum curator) British birdsDerek Oliver (theatre technical manager) The Second World War