At the farthest reaches of the British Empire, four men swear an oath to keep a terrible secret, a secret drenched in blood which is the key to immense wealth.

In London, Sherlock Holmes is suffering once more from the dreadful ennui which plagues him, when a beautiful young woman comes to him with a mystery which is to stretch even his remarkable deductive skills.

Once a year, Mary Morstan receives an anonymous package containing a magnificent costly pearl. Aware that the gifts are somehow connected to the disappearance of her father ten years previously, she is both intrigued and frightened by the arrival of a letter summoning her for a meeting in the dead of night. Accompanied by Holmes and Watson, Mary embarks on a quest which is to lead them through the dark heart of the city, to a one-legged man and an incredible tale of greed and revenge.