One of Sir Bohun Chantrey's great passions in life is the stories of Sherlock Holmes. To celebrate the great man's anniversary, he throws a party at which the guests are instructed to come as characters from the detective stories. But several of the guests are more interested in Sir Bohun's money, and when he announces that he is to marry a poor governess, things take a turn for the worse, not least when the Hound of the Baskervilles turns up... Fortunately the incomparable detective Mrs Bradley and her secretary Laura are amongst the guests and ready to investigate the deepening mystery.