In the late 19th century, Toronto city police Detective William Murdoch investigates the murder of a young girl found drugged and strangled in an alley in the red light district. The autopsy reveals the girl was pregnant but Murdoch doubts she was a doxie. Murdoch faces the challenge of investigating prominent members of Toronto society when she is identified as Therese Laporte, a chambermaid working for a wealthy family. When a possible witness to the murder is also killed, Murdoch learns that Therese was seen voluntarily getting into a carriage, as if she knew the occupant. With another witness in danger, Murdoch must stop the killer before he strikes again.