The penultimate programme saw Edmund Reid (played by Matthew Macfadyen) locked in the cells of Leman Street police station with all hope seemingly lost, but it was a scripting mistake that had viewers talking.
Show writers had written a sentence including the line "kilometres upstream", a measurement that did not exist when the period drama was set.
Viewers took to social media immediately, with one tweeting: "#RipperStreet kilometres? Have a word!"
"#Ripperstreet an anachronism in tonight's episode? Were kilometres in use in Victorian England?" posted another.
A third wrote: "He said '..kilometres upstream', Were kilometres invented then? Certainly not in common use in Victorian Britain or even now #RipperStreet."Related articles
BBCRipper Street season 5: Viewers BLAST 'monumental period mistake' in epic