After receiving the approval of Miss Hudson, landlady of 221B Baker Street, John H. Watson, recently returned from the Afghan War, becomes the housemate of consulting detective Sherlock Holmes, who himself is soon implicated in a serious crime.

Holmes is frustrated at the thought of there being a mastermind behind the Noahtic and Drebber cases whose identity eludes him. After an unsatisfying investigation into a third nobleman death, Holmes has a chance encounter on a train.