It's 1895 and Toronto City Council is considering changing its electricity supply from direct current (DC) to alternating current (AC) to take advantage of the new electric generation plant at Niagara Falls. There's a lot of money at stake and the owner of Toronto Electric and Light, Daniel Pratt, has been holding public demonstrations on the dangers of AC current by electrocuting dogs. When Miss Toronto Electric and Light, Alice Howard, is electrocuted at one of these demonstrations, Detective William Murdoch cannot help but wonder if she was murdered. Assisted by the local coroner Dr. Julia Ogden and inventor Nikola Tesla, Murdoch applies his scientific approach to policing to solve the crime. Constable George Crabtree meanwhile pursues his own theory that animal rights activists may have been behind the death.

Detective Murdoch investigates the murder of well-known Toronto lawyer Percy Pollack. The body is delivered in a trunk to Toronto Police Station No. 4 with an ominous note addressed to Inspector Thomas Brackenreid, who believes he may be the next victim. While the Inspector uses the more traditional police techniques, Murdoch takes a more scientific approach in solving the crime particularly in determining the time of death, which proves crucial to solving the murder. Meanwhile, Murdoch catches the eye of the Chief Constable who suggests to him that he may be the ideal candidate for the vacant Inspector position at Station No. 3.

When professional boxer Amos Robinson is shot at close range, Detective Murdoch finds himself not only trying to find the murderer but to clear his wife, Fanny, who is being held for the murder by the police. Robinson won his fight earlier that evening but the fight had been rigged for him to lose and some lost huge wagers. His contract was also about to be sold so both the seller and the buyers have lost money. The blood splatter evidence convinces him that Fanny is innocent so he looks to those surrounding the boxer where he finds are several suspects.

Detective Murdoch attends a séance hosted by a medium, Sarah Pensall, where he is told the location of a recently murdered young woman. Although he believes that Pensall and those like her are all charlatans, he soon finds himself investigating the murder of Iris Winston, a prominent member of the Toronto Paranormal Society, whose body is found exactly where Pensall foretold it to be. Assisted by Arthur Conan Doyle, the creator of Sherlock Holmes who is in Toronto to make a speech on spiritualism, Murdoch firmly believes there is a practical solution to the murder. Those beliefs are shaken however when Pensall tells him she has a message from his late fiancée, who died of consumption over a year ago.

When Wendell Merrick is killed in the church office on his wedding day, Detective Murdoch is on the case. He learns that Merrick was to be married to Eunice McGinty, a somewhat plain looking girls from Niagara Falls. Murdoch soon realizes that the wedding was a sham. The autopsy reveals that Merrick was a homosexual and that his marriage would allow him to inherit his half of his late father's estate. The obvious conclusion was that he was killed by his lover in a fit of jealously but when that man commits suicide, Murdoch believes that the crime has yet to be solved and he uncovers a far more elaborate plot with an altogether different motive.

Detective Murdoch finds himself investigating his own father, Harry, for murder when the body of John Delaney is found soon after the two had an argument in a pub. Harry had complained that the ratting contest in the pub was fixed and was thrown out on his ear. Murdoch's father is a drunkard and down and out and there is no love lost between the two. He believes his father was responsible for his mother's death and they have not seen each other for many years. In his investigation, Murdoch is helped by an idiot savant who works at the pub and has a fixation on time. Using that information, the detective builds a detailed time line for the crime, finally identifying the anomaly that leads to the killer.

Detective Murdoch faces an unusual case when the desiccated body of a man falls through the ceiling of the Grand Theater and onto the stage during a performance of Macbeth. Using dental records, the body is identified as that of Virgil Smart, the former owner of the theater who had died a year ago. Problem is, Smart is supposed to be buried and when they re-open his grave, they find the body of an unknown man. Murdoch suggests that Dr. Ogden attempt a facial reconstruction to identify the body. When Murdoch and Crabtree find a hidden room off Smart's office, a love nest, they believe they've found the site of his murder.

Det. Murdoch and Dr. Ogden investigate the death of Richard Hartley a member of the men's eight rowing team at the prestigious, and snobbish, King's Rowing Club. Hartley was a newly appointed member of the team, having displaced Horace Briggs, a blue collar working man who was not of the same class as the others. Murdoch learns that Hartley had recently had an argument with his coach, Hamilton Kane. To complicate matters, the Hartley's are a prestigious Toronto family with a great deal of influence. The autopsy reveals that he drowned, but had also been beaten. Using a new-fangled lie-detecting device and analyzing the content of his lungs provides Murdoch with the clues he needs to solve the case.

Detective Murdoch investigates the murder of Rod Grimsby, who was forced to drink varnish. What they also find at the crime scene is the man's son Harcourt Grimsby, a ventriloquist who does most of his talking through his puppet, Mycroft. The dead man was having an affair with his neighbor's wife so they have an obvious suspect, but Murdoch thinks the solution is far more complex. He is joined in his investigation by Arthur Conan Doyle, the creator of Sherlock Holmes, who has returned to Toronto with the intent of writing a new novel based on Murdoch's techniques. He also has another, far more personal reason for returning.

The police investigate the murder of Howard Rookwood, a well-known Toronto industrialist and philanthropist who was struck on the head just outside of his house. Rookwood was an active supporter of Baker House, a home that specializes in relocating underprivileged children from England to Canada and his own daughter was adopted. As Detective Murdoch examines the forensic evidence, he and Doctor Ogden conclude that a child, or children, may be the culprit. The true motivation and solution to the crime however is far darker.

Detective Murdoch investigates the murder of Dr. Francis Grout who was killed by a hooded and robed figure using a crossbow. The doctor worked at the Greyson Institute for the Mind that specializes in researching brain functions and those who have special skills not found among the general population. As the murders continue, the police must find the common link among them. Murdoch is shaken when medium Sarah Pensell tells him she has seen these murders in a vision. While she can't identify the robed figure, she is able to identify the killer's last victim - Murdoch.

With the visit of Queen Victoria's grandson, Prince Alfred, to Toronto, Detective Murdoch and Constable Crabtree are put in charge of security. The Prince is a bon vivant who is particularly fond of parties and pretty girls but his aide, David Jennings, is hard-nosed and demanding. When the police find a dead girl in the park, her tattoos reveal that she may have been a member of the Irish Republican Brotherhood and there may in fact be a plot against the Prince. Murdoch also runs into to an old friend from their days at the seminary who may, or may not, have Republican sympathies as well.

Murdoch and Crabtree investigate the strange murder of Henri Gaston, who is found lying in the upper limbs of a very tall tree. There were no footprints leading up to tree so they have no theories as to how he may have gotten there. Gaston was an avid astronomer with a particular fascination about Mars and Constable Crabtree begins to think that Martians may be responsible. Murdoch however suspects a more human perpetrator, especially when he learns that Gaston was refusing to sell his land to a developer. What they eventually stumble upon is something that is completely alien to their experience.