Nigel Strangeways, private investigator, is invited to spend Christmas with flying ace, Fergus O'Brian, who has rented the Dower House from his aunt and uncle. Fergus's life appears to be under threat from an anonymous letter writer. Nigel finds himself part of a Christmas house party with a selection of people who might or might not be the letter writer. When Fergus is found shot dead with his own revolver on Boxing Day morning in circumstances which indicate it may have been suicide Nigel is faced with a complex case to unravel. But first he has to convince the local police that it isn't suicide.