There has always been an air of incipient doom hovering over Ripper Street, since the show is more of a laboratory of lost souls than a mere detective drama.

H Division has a new home in Whitechapel that basks in the white heat of the technological revolution. The police station not only has a telephone but a “microreader” that allows the user to check thousands of miniaturised card indexes. Alas, a wry smile is all the viewer is likely to get from this opening episode of the fourth season. Nothing happens until the last ten minutes.

Axed by the BBC at the end of 2013 after its second series, ostensibly because of poor viewing figures, Ripper Street found a new home on Amazon Prime, where the third series began streaming in November last year. With a fourth and fifth series already commissioned by Amazon, the BBC is making up for lost time by airing Series Three. Perhaps the Top Gear bunch will be back on the Beeb yet.

Though greeted ambivalently when it made its debut at the end of 2012, Ripper Street has looked increasingly like TV's undervalued secret weapon as it has surged purposefully through this second series. Maybe the title was misjudged, suggesting it was just another gruesome and mist-shrouded Victorian murder mystery. Turns out it was much more than that.

Proof that the BBC’s love of gritty realism is not solely the province of Luther and similar modern-day urban crime dramas comes just minutes into the second series of Ripper Street, before the credits even roll. In the East End of London a police officer is thrown from a window, only missing a little boy playing recorder for the amusement of the street below when his leg is gruesomely impaled on a railing.

Last week we left Homer Jackson, the raffish ex-Pinkerton detective with the exceedingly chequered past, languishing in jail, after being fitted up for a Ripper-style killing by the murderous Frank Goodnight (played by cultish US actor Edoardo Ballerini). For this week's finale, Matthew Macfadyen's DI Reid urgently needed to get Jackson out again in order to apply his advanced forensic skills to unravelling a white slaving racket.

Perpetually reborn in movies and TV series, Jack the Ripper rides again in Ripper Street, which is set in Whitechapel in 1889, in the aftermath of the much-mythologised murders. Except this time, the subject isn't the Ripper himself so much as the dread and hysteria he left in his wake, which shrouds the murky streets like poison gas.