An evil stalks London, blown in from the tropics. Stories of cursed giant rats and malign spirits haunt the garrets of the East London neighborhood of Limehouse. A group of merchants are dying one by one. The elementary choice to investigate these mysterious deaths is, of course, the team of Holmes and Dr. Watson. But the unique gifts of their housekeeper, Mrs. Hudson, and her orphaned assistant Flotsam, will also be needed to solve the case. Can she do it all under the nose of Sherlock himself?