Seeking a holiday gift for their landlady, Mrs. Hudson, Sherlock Holmes takes Dr. John Watson to Whiteley’s, where screams and blood alert them to a startling tableau: A man is dangling from the upper branches of the half-decorated Christmas tree adorning the emporium’s main floor. Inspector Darke, the Metropolitan Police officer called to the scene by officious owner William Whiteley, pronounces Albert Robinson’s death accidental even before his body has been taken down and identified, but Holmes quietly corrects him: The carotid artery of Whiteley’s jack-of-all-trades has been cut. The reciprocal expressions of condescension between Holmes and the Met continue as the day unfolds, with Darke and his colleagues dismissing the amateur detectives as bunglers out past their depth and Holmes imperturbably calling them out time after time. He has plenty of chances to do so, because another corpse, that of socialist postman Jonathan Orman, is found hanged in a Regent’s Park changing room very soon thereafter, and retracing Orman’s steps that morning promptly leads to the discovery of author Sarah Martin, her throat cut and her mouth crammed full of Christmas pudding, and the undiscovered Jenny Martin, her missing niece and housemate. Holmes links all the murders (a fourth will follow) to the Christmas holiday and a long-ago scandal without breaking a sweat, winning the grudging acclaim of Inspector Darke and delighting fans who’ve been waiting for another Sherlockian Christmas ever since “The Adventure of the Blue Carbuncle.”