Escaping from Bedlam after three years, Marlott embarks on a quest for revenge against Hervey, as the murder of an archdeacon shocks London.
Suspecting that the clergy killings are linked to Hervey, Marlott takes refuge under an alias in the slums and finds work collecting plague corpses.
Public outrage over the clergy murders mounts as Marlott grows closer to widowed seamstress Esther and interrogates his former nemesis, Billy Oates.
Marlott suspects his allies are in danger after an encounter with mysterious aristocrat Frederick Dipple; Spence reveals the truth about the plague.
Boz confirms that Hervey is still alive, leading Marlott into danger at a supposedly deserted tower owned by Dipple and used to store blocks of ice.
Captured and chained, Marlott must free himself and rescue Esther from Hervey, while rival law enforcement factions unite to apprehend Dipple.