Whitechapel, Series Four, ITV1

I can’t have been alone in my struggle to keep the two of them straight in my head: there’s the one set in the east end of London, in which a former BBC Spook tries to track down Jack the Ripper; and then there’s the one set in the east end of London, in which a former BBC Spook tries to track down a modern-day killer inspired by Jack the Ripper.

When Rupert Penry-Jones, dressed in suave black tie like the James Bond he never was, arrived at the book launch that kicked off this fourth series of Whitechapel, it took a few minutes - and a bit of stylised violence in an alley involving a kid in a thoroughly modern hoodie - for this newcomer to adjust her expectations to the correct decade.

The show relies on the interplay between its three male leads as much as the suspense

Of course, ITV’s other flagship crime drama of recent times cut its ties from the 19th-century serial killer at the end of its first series, but in the week of the 125th anniversary of his first real-life victim the Ripper’s is one of the many ghosts that lingers around the precinct of coppers Chandler (Penry-Jones) and Miles (Phil Davis). Although this new series purports to keep to the formula established last year, when the three episode arc was replaced by three two-part stories, there are hints of threads that may yet tie the whole thing together. Chief among them is that book on the titular area of London by Ed Buchan, the historian and police consultant played by Steve Pemberton (pictured below right); and a chilling warning given by the former spy who is the prime suspect in this week’s action. Apparently the reason that history keeps repeating itself in Whitechapel - with the team’s previous successes inspired by the crimes of Ripper and the Kray Twins, as well as the lesser-known influences that cropped up 18 months ago - is because the area is some grey, English equivalent of the Hellmouth of Buffy the Vampire Slayer fame.

Our first victim is an “old dosser” of Bulgarian origin who seems to have died in the most horrific way possible: after falling through a roof and breaking both of his ankles, the better not to escape, both he and his pet rat are slowly crushed to death - a mimicry of a form of 16th-century torture used against those accused of witchcraft. The team are used to seeing gruesome deaths, but it is that of the rat - force-fed stones by the killer - that reduces Claire Rushbrook’s pathologist to tears. “Hormones,” she says sniffily, apropos of nothing at all.

The writers of Whitechapel may excel at picking the parts they like from different genres and combining them in unexpected ways, but on the evidence of this first hour at least they’re not particularly interested in the diversity of character that defined shows like - well, Buffy the Vampire Slayer. This particular storyline’s leading lady is Stella Knight from MI6 (Daisy Beaumont), and when she finally shows up in response to the police uncovering the first victim’s true identity she’s an obstructive cartoon character in red lipstick and heels.

Of course the show relies on the interplay between its three male leads as much as the suspense - and the odd irresistible hat-tip towards Penry-Jones’ best-known role - but with both charisma and light relief in short supply for now I found it hard to keep track of a seemingly endless procession of whey-faced, brooding men against a series of dimly-lit backgrounds (there’s a romantic sub-plot involving a detective constable’s sister that completely passed me by). It takes the arrival of a second victim, apparently burned at the stake, to begin to make sense of it all.