Sir Clinton Driffield Mystery series #2

At Ravensthorpe - a lonely country house inherited by Maurice Chacewater - a masked ball is in progress amid scenes of great gaiety, celebrating the honor of his sister's coming of age. What each guest was to wear had been kept a secret and all who enter Ravensthorpe that night wear masks. Cecil, who is on bad terms with his brother Maurice, arranges a practical joke with several young friends to plunge Ravensthorpe into darkness and to carry out a mock burglary at a given moment; but the plan is overheard. The ensuing situation is doubly complicated. In the drama that follows, the theft of rare Leonardo da Vinci medallions, thrilling chases through the woods, secret passages, suicides and murders, all have their places. Everything is woven into one complex and exciting pattern, and the final unravelment by Sir Clinton Driffield is masterly.
-from Amazon