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.

When Constable Oliver Wicken is found shot through the head in the basement of an abandoned house, everyone but Detective Murdoch seems satisfied to put it down to suicide. A gun and a note were found on the scene but the trajectory of the bullet raises doubt. Using unproven techniques such as taking fingerprints off the weapon, Murdoch satisfies himself that he has a case of murder. Working with the medical examiner, Dr. Julia Ogden, he is able to demonstrate that Wicken had been in proximity to a blond woman prior to his death. When Murdoch learns that Wicken was secretly engaged, he has a new line of inquiry to pursue. The solution however is found thanks to Murdoch thoroughness and his investigative skills.

Detective Murdoch investigates the murder of Dolly Capshaw, a mid-wife who, it turns out, was also an abortionist. Using knew techniques such as fingerprints (or finger marks as they are known at the time) and handwriting analysis, Murdoch eliminates a number of suspects but has proof that a self-righteous and nosy neighbor, Mr. Golding, was in the house. Missing from Capshaw's desk is her register of clients, a large red book with the image of a dragon on the cover. Murdoch's investigation involves many people whose lives had, in one way or another, crossed with Capshaw's including Ettie Weston, who is no longer a prostitute but is now on the stage with a mentalist act and Maude Pedlow, the wife of a prominent Superior Court judge. Meanwhile, Constable George Crabtree is in training for the Toronto police boxing tournament under the tutelage of Inspector Ramsgate.