The Finishing Stroke By Ellery Queen

At the tail end of the Roaring Twenties, a birthday bash for publishing heir John Sebastian, Jr., perfectly coincides with the twelve days of Christmas. Among the twelve invited guests is Ellery Queen, a newly published mystery writer planning to enjoy every last minute. But when an uninvited Santa Claus shows up on Christmas Eve and then mysteriously goes missing, the party takes a disturbing turn. Threatening clues masked as gifts begin to appear under the tree, and Queen - a novice crime fighter on his first solo case - must try to solve the killer's puzzle before someone gets murdered. After a dead body turns up, Queen is no closer to stopping the killer. If he can’t anticipate the next clue before it shows up, John Sebastian’s birthday will end up his funeral.