Sir Anthony Blunt (Fox) is an internationally respected art expert who also serves as an art adviser to Queen Elizabeth II. His life unravels when an on-going British Intelligence investigation reveals him to be the fourth man in the Burgess-Maclean-Philby scandal involving Englishmen who spied for, and eventually defected to, the USSR. The investigation of Blunt's covert past is paralleled with his own art investigation of a painting attributed to Titian. Three men are depicted in the art work--with a fourth male figure discovered to have been painted over. Alan Bennett adapted his play for this TV drama.