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.
Detective Murdoch lets crime author Arthur Conan Doyle, who needs inspiration for a new (post?) Sherlock Holmes book, join his investigation of the murder of Rod Grimsby, poisoned with varnish, perhaps for adultery with his neighbor Stanley Paulk's wife Emma. Rod's son, ventriloquist Harcourt Grimsby, found on the spot with his insuperable dummy Mycroft, puzzles Murdoch, who works out an extraordinary motive and further upheavals in the honor murder theory.
When a drunken, philandering wastrel is found dead in his room, having had varnish forced down in his throat, his estranged disturbed ventriloquist son is found in a wardrobe.
- Roddy Grimesby is found dead from a lethal ingestion of varnish. When the police show up at the crime scene, the victims son Harcourt a ventriloquist is found hiding in the closet with his look-alike dummy Mycroft. Even more disturbing than the similarity, is the roiling bond between the two much like hostile brothers. Although Harcourt confesses to the murder, Murdoch spots inconsistencies in the story that make no sense unless there was a third party involved. Harcourt had been in the room when Roddy was killed. He would have seen the killer, but why is he protecting his identity? In a shocking turn, Murdoch learns that Harcourt has a twin brother named Mycroft. Maybe Mycroft killed Roddy; and Harcourt is protecting him. But just when it looks like the case is solved, Murdoch sees something in a Grimesby family photo that puts a whole new twist on things.