Three years have passed since the death of Holmes. Dr. Watson married Mrs. Hudson, his stories about the famous detective are successfully reprinted. A small memorial museum opened in Baker Street. But life without adventure is boring. Therefore, when one day a young girl turns to the doctor with the old memory asking him to reveal the cause of her lover's death, Mrs. Hudson equips Watson for the case. This case is preparing him a lot of surprises and shocks. It turns out that the killing of the clerk is connected with the disappearance of secret documents, and we can talk about the impending assassination attempt on the Queen of England. To prevent an attacker from accomplishing this, Dr. Watson needs a reliable assistant.