Mr Medlicott, a solicitor, heads to the country home of his old friend and client Sir John Wynward, to spend Christmas with Sir John's family and friends. But after a peaceful and enjoyable Christmas for all apart from Medlicott himself, Sir John dies on Boxing Night, sitting at his desk in his study - to all appearances, a heart attack. But natural death is out of the question when both Medlicott and Gooch, the chauffeur, are found murdered. What was Medlicott so afraid of? What did Gooch know that got him killed? Who is the mysterious "Mr Levi", who sent notes to the victims demanding the diamond?

Exit Sir John was first published in 1947.