In August 2010 Shaftesbury Films announced that production on the fourth season of Murdoch Mysteries had begun and was scheduled to continue through November 2010. Guest stars in season four include Victor Garber, Lisa Faulkner, Simon Williams, Peter Keleghan, Craig Olejnik, and Lisa Ray. On October 15, 2010 Canadian Prime Minister Stephen Harper and his daughter visited the set of Murdoch Mysteries. As part of the visit to the set Stephen Harper filmed a cameo appearance.
Murdoch makes headlines again in Toronto for his use of a new device he’s invented, a Scrutiny Camera which takes photos at night without a flash.
Murdoch dismisses Crabtree’s idea for a board game involving clues about the identity of a murder, his murder weapon, and the location of the crime, saying “I’m sure people would find murder far too grave a subject of frivolous entertainment.” (ep.404)
Julia pours green Jell-O, "... all the rage in Buffalo", into a head wound of a corpse to obtain a mold of the lethal weapon, without it adhering to the brain tissue. (ep.404)
Murdoch invents a way to transmit photographs across continents. Crabtree envisions the creation of devices known as “Tele Facsimile Machines.” (ep.405)
August 1898, Murdoch creates the Graphizer, which uses sound waves to find sunken boats in Lake Ontario.(ep.407)
When telephone technology is still in its infancy, Detective Murdoch uses a recording device to wiretap the phone calls. (ep.408)
Murdoch crafts sn attachment to help solve a mysterious shooting in which no one heard the shot. He calls it a “muffler” but Constable Crabtree says that “silencer” has a better ring to it. (ep.409)
October 1898, Murdoch invents the Dye Discharger, based upon the model of a mouse trap, which when triggered, blasts red paint all over a criminal’s hands, marking him as the culprit. (ep.412)
The discovery of dismembered body parts encased in a concrete block poses a seemingly impenetrable mystery, but Murdoch chips away at the case, despite the resistance of prickly pathologist Dr. Llewellyn Francis.
A dead soldier found hanging from a tree with his head twisted 180 degrees points Murdoch to a secret plot in the Canadian military. The investigation puts the constabulary at odds with both the British and Canadian armed forces.
Murdoch reunites with his old flame, Dr. Julia Ogden, in Buffalo, New York, to investigate the death of a young patient. In short order, Murdoch's feelings for Julia heat up, as do suspicions surrounding one of Ogden's colleagues.
Wealthy patriarch Percival Jenkins is found facedown in a bowl of porridge, pulling Murdoch into a world of privilege and resentment. Murdoch untangles the twisted web connecting the servants and family members and finds that each has a motive to kill.
The disappearance of a visiting Parisian girl thrusts Murdoch into an odd partnership with French Detective Marcel Guillaume, a real-life inspiration for the fictional Inspector Maigret. Brackenreid, meanwhile, ponders a political career.
Murdoch suspects that a detailed miniature streetscape of a Toronto neighborhood contains clues to a homicide. But the artist is an idiot savant, unable to finger the killer. It's up to Murdoch to get a clear picture of a street roiling with conflict, deceit, and murder.
A phone operator with a penchant for amateur sleuthing claims she overheard the strangulation death of a young woman. Is the wannabe detective crying wolf? Murdoch taps into the phone system to prevent a killer from striking again.
Murdoch's old friend Anna Fulford gets engaged to a New York businessman, but plans for Niagara nuptials come crashing down when Anna's fiance turns up dead. Murdoch suspects the Black Hand, a ruthless pre-Mafia organization.
A dashing masked robber steals from banks and gives to the poor la Robin Hood, but Toronto is no Sherwood Forest. Undaunted by the sensational reporting of Paddy Glynn or the detective's longing for soon-to-be-wed Dr. Ogden, Murdoch probes the crimes.