Mary Morstan has received a pearl in the post every year since her father’s disappearance; this leads Holmes and Watson to the truth about a secret pact between four convicts during the Indian Rebellion of 1857.

For years, a blackmailer has been preying on the weaknesses of others throughout London. When Holmes hears of the utter misery this mystery man is creating, he adopts a campaign to thwart his evil scheming. The campaign astonishes Dr. Watson by its strangeness and finds Holmes falling in love.

Sherlock Holmes’ problem with disturbing dreams proves to be both an impediment and an aid in the search for a missing woman.