1877: The Pinkerton detective Celeste Summersteen travels with young Dorothea Ellingsford from Chicago to London. Ostensibly, she is to return the girl to her family, but her real mission is more delicate: One of Dorothea's friends has been murdered, and the detective must find the killer, as Dorothea herself may be in danger. However, the investigation proves difficult: The girl remains stubbornly silent, and the only clues to the murderer are a piece of fabric and a lock of hair found in the mouth of the deceased. Then, the body of the Opium Queen of the East End is discovered in the Thames. In her search for answers, Celeste must delve deep into the corrupt heart of London, risking her own life in the process. Meanwhile, Inspector Edwards from Scotland Yard, who is supposed to assist her in the investigation, is anything but helpful.