Factual error: Inspector Rusk uses the term "trope" in its modern meaning of a theme or motif. This usage did not come into vogue until the late 20th century; the first such usage recorded by the OED was in 1975. The series is set in the 1890s and the language used is generally that of the time.
Factual error: Inspector Rusk lost an arm while serving in the army before he became a policeman. A one-armed man would never have been allowed to join the police in Victorian England - as today, all police officers had to join as uniformed constables and they had to be completely physically fit and able-bodied. Only the most senior officers (well above inspector) could join directly in a senior rank.