The Serpent is the best BBC drama series in ages — god knows how it slipped through the net — but I still think it most unlikely that I shall stick it through to the final episode. It’s not the style that’s wrong but the subject matter: do we really want to spend eight hours of life in the company of a smug, ruthless serial killer who murders at least 12 people — and more or less gets away with it?

Up to a point The Serpenthas addressed this problem by trying to make the central figure not the killer, Charles Sobhraj, but the persistent Dutch junior diplomat, Herman Knippenberg, who eventually nabs him. But that still doesn’t quite remove the nasty taste you get from watching dreamy-eyed innocents on the hippy trail being seduced by Sobhraj’s patter, prior to being brutally killed in any number of hideous ways, including drowning, strangulation and being burned alive.

It’s especially painful viewing for those of us of a certain age, who might conceivably have found themselves in scenarios like the one so cruelly exploited by Sobhraj. You’re young, naive and on a budget, somewhere remote and exotic like Bangkok, and — hungry for new experiences while trying to save money in order to eke out your adventure — you’re piteously vulnerable to friendly-seeming con men such as Sobhraj, who only want to invite you back to their pool party-friendly apartment out of the goodness of their heart.

One of the early victims was an American backpacker, determined to have just 12 hours more fun before heading to Nepal to sequester herself as a Buddhist nun. Bad mistake! How you felt her helplessness and impotent fury as, taken to a sex club by Sobhraj, she succumbed to the sedatives he’d slipped into her drink, knowing — like some slow-motion horror movie suddenly experienced for real — there was no way she was going to get out of this alive.

Equally well captured was the decadence and indifference of 1970s diplomatic staff. The boozed-up young Aussie attaché, not giving a damn about missing backpackers because, as long-haired hippies, they deserved whatever was coming to them. The Dutch and British ambassadors sprawling at the tennis club. Knippenberg berated by his boss (on the way out with his golf clubs) for fussing over a matter best handed over to the local police.

A bit like with The Queen’s Gambit,all the period detail — those huge-framed 1970s sunglasses, the curfews passed by drinking right through the night, the seedy backpackers’ hotels, passport control, the flight numbers on the boards — was so perfectly done, so redolent of a lost (and mostly, barring the odd serial killer, more glamorous and desirable) era that it almost didn’t matter what the plot was doing. But will the nostalgia and all that visual feasting be enough to carry us through? Perhaps. What I’m very much appreciating — so unusual these days from the BBC — is the absence of unnecessary politics, and superb casting that is honest and appropriate to the era.

Jenna Coleman is first rate as the killer’s initially ice-cool but increasingly trepidatious French-Canadian girlfriend; but Tahar Rahim has a more difficult job fleshing out the sinister, apparently charismatic Sobhraj, who remains largely unknowable. Sobhraj is still alive by the way — now 76 — and married to a woman four decades his junior, who once appeared on the Indian reality show Big Boss. He’s living in great comfort in a Nepalese prison, which brings me back to my initial reservation: can it really be right that we spend quite so much viewing time reliving this unrepentant monster’s depravities?

Still, better eight hours of The Serpent than even half an hour in Bridgerton, Netflix’s new colour blind, sub-sub-Jane-Austen costume drama romp. I gather that millennials and Gen-Zs are happy to take it for what is is: frothy, Regency-era porn with smouldering dukes who look like rap stars, bags of the vigorous sex that never quite made it into Emma or Northanger Abbey, women shrieking as they die in childbirth and so on.

But if you’re old enough to remember, say, the Jennifer Ehle and Colin Firth version of Pride and Prejudice — that’s a quarter of a century ago, rather horrifyingly — I doubt you’ll get past the fundamental plausibility problem: how, in an era of history when social nuance can rarely have been more acute, when a fake accent, an inappropriate bonnet or the whiff of trade can be spotted and dismissed at 1,000 paces, does not a single character notice another’s skin colour?