The Serpent, episode 2 review: never mind the charmless killer, it's 1970s Bangkok that most impresses

The problem with The Serpent (BBC One) is that it is a whodunit where we already know who did it. As this retelling of the true story of Seventies serial killer Charles Sobhraj meandered through the second of eight episodes, no attempt was made to conceal the French ex-pat’s criminality or to cloak him in a veil of mystery. He was a greedy, grubby sociopath preying on naive backpackers travelling to Thailand in search of a hippy paradise.

The strength of the drama instead flowed from its evocation of the Bangkok of half a century ago. The thrill of the tourist trail was rivetingly recreated. But while part two of The Serpent came into its own as a snapshot of the past, it was less compelling when the action switched back to the charisma-free Sobhraj, busy drugging and robbing unsuspecting hostel-hoppers.

One way in which the series has tried to bring a fresh perspective to the case – which has already inspired three nonfiction books, a Bollywood movie and an episode of Law and Order: Criminal Intent – is by framing it from the vantage point of Sobhraj’s girlfriend, Marie-Andrée Leclerc. Of course this choice may also have something to do with the fact that Leclerc is portrayed by Jenna Coleman, by far the most famous cast member.

As with the first episode, her biggest challenge was Leclerc’s French-Canadian accent. She did her best. But you were never not aware that you were watching Jenna Coleman. That may not have been entirely her fault. The script by Richard Warlow and Toby Finlay so far failed to put any flesh and bones on either Leclerc or Sobhraj (Tahar Rahim), whose most memorable attribute were his retro Seventies glasses.

It is true that some rudimentary psychoanalysis has been attempted on Sobhraj, who back in Paris was never allowed forget his mixed Vietnamese-Indian heritage. But The Serpent seemed generally determined to depict him as a blank space, which hasn’t given Rahim much to work with.

That remained so even during a flashback to the beginning of his relationship with Leclerc, who was shown mooching around Kashmir with an ex-fiancé. Posing as a photographer, Sobhraj seduced her with his movie star looks and understated charm (so understated that it didn’t come across on screen).

Only later in Bangkok did it dawn on her that he wasn’t all that he appeared, as he was revealed to have a local lover whose father was prominent in the military. Sobhraj’s violent nature, meanwhile, became clear as he and sidekick Ajay Chowdhury (Amesh Edireweera) turned on the Dutch backpackers they’d been poisoning.

It was the travelogue elements that impressed most. Seventies Bangkok was a wonderful playground in which to become lost. The dissolute world inhabited by Western diplomats was conjured with particular vividness.

Here, Tim McInnerny shone as gruff Belgian attaché Siemons. He was providing grudging assistance to idealistic Dutch diplomat Herman Knippenberg (Billy Howle), in his investigation into the disappearance of the backpackers.

Knippenberg had become convinced a killer was targeting tourists. But Thai authorities were indifferent while the higher-ups at the embassies were scornful of the “long-hairs” swanning into Bangkok. The only hope was a tip-off from a mysterious French woman who appeared to have knowledge of Sobhraj’s deeds.

These scenes of Knippenberg negotiating the sweltering underbelly of Thailand were hugely atmospheric (and all the more impressive given that production was required to move from Thailand to Hertfordshire during the spring). But they couldn’t compensate for a serial killer drama in which the essential thriller component appeared to have evaporated in Bangkok’s pummelling heat.