Everyone loves a ripping yarn. A tale of murder most horrid and dastardly deeds on the streets of olde London town. Ripper Street taps into the world of penny dreadfuls, Hammer Horror and Sherlock Holmes. However it hasn't been plain sailing for the period detective drama, a dip in ratings saw the show cancelled after two series until Amazon stepped in to split the costs. They seem to be happy with their BBC co-production and have already confirmed a fifth season for 2017.

With Queen Victoria's Diamond Jubilee as a backdrop it's 1897 and three years have passed since the end of series three. And much has changed. Edmund Reid (Matthew Macfadyen) has moved to the coast with his daughter after their recent reconciliation; Drake (Jerome Flynn) finds himself as the new Detective Inspector overseeing the slow modernisation of the London police force (they even have one of those new-fangled telephone thingamajigs); Susan (MyAnna Burning) languishes in prison awaiting a death sentence while Captain Jackson (Adam Rothberg) tries to save his wife from the hangman's noose.

Unfortunately Reid can't escape his past as the conviction of the Whitechapel Golem is called into question. Meanwhile on the banks of the Thames the body of a young Indian is found with his throat slit (which opens up a timely look at historical racial tension and immigration). Soon Reid has (literally) dusted down his bowler hat and headed back to London to fight the good fight.

Ripper Street started strong but series three hit a rut and this opening double bill (entitled 'The Stranger's Home') continues the trend. Despite the grisly murders and bodice ripping sauce it fails to catch the imagination. It's hard to pinpoint exactly where the fault lies. The three leads are superb: Macfadyen is stoic, brooding and resolute; Flynn's gruff exterior hides his soft hearted core; Rothenberg's portrayal of tortured love drips with authentic desperation. But it's too serious, everyone is dour and miserable, the story plods rather than sizzles. The building blocks are there but as a whole Ripper Street amounts to less than the sum of its parts, it's merely adequate rather than gripping.

Ripper Street Series 4 starts on BBC Two, Mon 22 Aug, 9pm.