London, 1932. When Harriet White rebuffs the advances of her boss at the Baker Street building society where she works, she finds herself demoted to a new position... a very unusual position. Deep in the postal department beneath the bank, she is tasked with working her way through a mountain of correspondence addressed to Baker Street's most famous resident: Mr Sherlock Holmes. Seemingly undeterred by the fact that Sherlock Holmes doesn't exist, letter after letter arrives, beseeching him to help solve mysteries, and Harry diligently replies to each writer with the same response: Mr Holmes has retired from detective work and now lives in Sussex, keeping bees. Until one entreaty catches her eye. It's from a village around five miles from Harry's family estate, about a young woman who went to London to work as a domestic, then disappeared soon afterwards in strange circumstances. Intrigued, Harry decides, just this once, to take matters into her own hands. And so, the case of the missing maid is opened...