O utdoor drama is a pleasure complicated by the plot twists of the season. A day of almost hourly showers left the evening air so ominously moist for Sherlock Holmes that the detective could reasonably have announced: “The rain’s afoot.” A deluge held off but gave way to such coldness that the smoke and dry ice in the production competed with the actors’ breath clouds. Billed as “a new mystery”, the script by Joel Horwood is a sort of bridge between Conan Doyle’s A Study in Scarlet (1887) and The Sign of the Four (1890). The conceit is that we are seeing the “real” events that Dr Watson, frantically transcribing most of the play’s dialogue into a notebook, later published as the second Sherlock Holmes book. But while he faithfully recorded some of the case – including jewels from an Indian Mughal treasure box sent annually to Miss Mary Morstan in London – we see that he falsified elements including the true persona of Holmes.…