One is Nicholas Blake's Thou Shell of Death (1936). Nicholas Blake is the pseudonym of Cecil Day Lewis, late British poet laureate.
Thou Shell of Death features Fergus O'Brien, WWI flying ace. Fergus receives four letters predicting that he will be murdered on Boxing Day. Despite this, or maybe because of this, he plans a party and invites all the suspects (there are several people who might want to do him in) plus private detective Nigel Strangeways. O'Brien does die, and it's up to Nigel Strangeways with the help of Inspector Blount of Scotland Yard to solve the crime. This is Blount's first appearance in the series. Thou Shell of Death is an oldie but goodie, especially if you like houseparty mysteries.
There are three other novels that focus on Boxing Day. A frozen body is found on Boxing Day in Viveca Sten's In Harm's Way. Another mystery is Gilbert Adair's The Act of Roger Murgatroyd that takes place entirely on Boxing Day. This is part of his series of novels about Evadne Mount, and is clearly a play on Agatha Christie novels. In another Boxing Day mystery, Death at Sandringham House by C.C. Benison, Her Majesty the Queen, along with her housemaid Jane Bee, investigates.
And, if you're unfamiliar with Boxing Day, it's the day after Christmas, when "servants and tradesmen traditionally would receive gifts from their superiors." Today it's a national holiday in most of the British Commonwealth and former British colonies. As far as why it's called Boxing Day, there are several different theories:
A ‘Christmas Box’ in Britain is a name for a Christmas present.
Boxing Day was a day off for servants and when they received a ‘Christmas Box’ from the master. The servants would also go home to give ‘Christmas Boxes’ to their families.
A box to collect money for the poor was placed in Churches on Christmas day then opened the next day.
Great sailing ships when setting sail would have a sealed box containing money on board for good luck. If the voyage were a success the box was given to a priest, opened at Christmas and the contents given to the poor.
Are there any other Boxing Day Mysteries I've forgotten?
And, if you're not tired of cooking and baking, today is also Candy Cane Day. If you have any candy canes lying around, try this recipe for Candy Cane Truffles.