Rising War Office star Mycroft Holmes persuades his brother, Sherlock, to volunteer at a friend's orphanage, where the suspicious death of a street urchin and a mysterious Chinese woman lead the brothers into the London opium trade's dark underside.
When his fiancée abruptly departs for Trinidad after hearing disturbing news, Mycroft Holmes and his best friend Cyrus Douglas follow and find themselves drawn in to a treacherous investigation.