Professor Willingdon (Barry Jones) is a scientist engaged on highly secret Government research. When he sends a letter to 10 Downing St threatening to blow up the Houses of Parliament within 7 days unless the Prime Minister agrees to his demands, it is first dismissed as a hoax. When Willingdon disappears however, alarm bells ring, and soon the whole of London has joined in the manhunt for this modern day Guy Fawkes. Also starring Joan Hickson, the film won the Oscar for Best Screenplay that year.