While Sherlock takes a little time out to study in the countryside, Watson has gone missing back in London. He enlists the help of Watson's fiancé, Miss Mary Morstan, to uncover the mystery.
An early form of the Suffragette movement has begun and its causing great concern in the corridors of power. These woman appear to stop at nothing for the vote but is that all they want? Mary Morstan is on the case.
Mary's ex-employer Mrs. Cecil Forrester comes to her for help after being blackmailed for thousands by the notorious Charles Augustus Milverton. Mary has to find something that will prevent Mrs. Cecil Forrester's secret from being revealed.