On the surface, life is going well for Victorian special agent Sir Maurice Newbury, who has brilliantly solved several nigh-impossible cases for Queen Victoria with his indomitable assistant, Miss Veronica Hobbes, by his side. But these facts haven't stopped Newbury from succumbing increasingly frequently to his dire flirtation with the lure of opium. His addiction is fueled in part by his ill-gotten knowledge of Veronica's secret relationship with the queen, which Newbury fears must be some kind of betrayal. Veronica, consumed by worry and care for her prophetic but physically fragile sister, Amelia, has no idea that she is a catalyst for Newbury's steadily worsening condition.
Veronica and Newbury's dear friend Bainbridge, the chief investigator at Scotland Yard, tries to cover for him as much as possible, but when the body of a well-known criminal turns up, Bainbridge and Veronica track Newbury down in an opium den and drag him out to help them with the case. The body clearly, irrefutably, belongs to the man in question, but shortly after his body is brought to the morgue, a crime is discovered that bears all the dead man's hallmarks. Bainbridge and Veronica fear someone is committing copycat crimes, but Newbury is not sure. Somehow, the details are too perfect for it to be the work of a copycat. But how can a dead man commit a crime?