The Serpent's Ellie Bamber on serial killers, Dominic West and Mandy Rice-Davies

“My generation has a huge hunger for true crime stories,” says Ellie Bamber. “Perhaps we’re more keenly aware now, that parts of us all are dark and flawed? But our interest in serial killers is about looking beyond that, peering into acts that are incomprehensible, picking through the brains of these mad individuals…”

With her bubbly attitude – and endearing tendency to use quaint terms like “super duper” – the 23-year-old actor doesn’t strike me as murder junkie. But she assures me that she spent lockdown watching shows like Netflix’s Mindhunter (based on real-life FBI profiler John Douglas) with friends via Zoom – “so we can analyse things together”.

According to AskWonder, the average consumer of TV crime series is a college-educated millennial woman (18-34 years) who is more interested in psychological analysis than action. They’re drawn to survivor tales and more likely to engage with true crime when the victim is female. And Bamber – best known for playing a winsome Cosette in the BBC’s 2019 Les Misérables – has a plum role in the latest TV series to tick all those boxes.

The Serpent – an eight-part BBC drama written by Ripper Street’s Richard Warlow and filmed mostly in Bangkok last year – is a darkly seductive dramatisation of the crimes of Charles Sobhraj, the Vietnam-born French psychopath who murdered an unknown number of western tourists on the hippy trails of south-east Asia in the 1970s.

Handsome and manipulative, he “befriended” travellers in Thailand, Nepal and India, often offering them cut-price jewels and lavish hospitality. Then he would drug them with anything from diarrhoea-inducing pills to itching powder before robbing and, in around 24 cases, killing them. He bludgeoned, stabbed and shot his victims, then often disfigured their corpses. Because his victims were mostly “longhairs”, prone to wandering off grid, the authorities didn’t pay much attention.

Sobhraj’s killing spree was only exposed by a tenacious Dutch diplomat in Bangkok called Herman Knippenberg. Moved by letters from the distressed parents of a young couple who had disappeared, Knippenberg realised they had been strangled and burnt alive after meeting a mysterious “gem dealer”. The Serpent makes a point of contrasting the quiet, methodical decency of Knippenberg (played by Billy Howle) with the flashy, impulsive, cold-heartedness of Sobhraj (Tahar Rahim). Bamber plays Knippenberg’s clever German wife, Angela, who supports her husband every step of the way.

The couple’s wholesome goodness glows from the screen, and rescues the series from glamorising the sinister-but-stylish world of Sobhraj. But viewers are still likely to feel a frisson of discomfort at the way the murders of these real young people have been turned into such slickly binge-watchable entertainment. Take Teresa Knowlton, a gutsy 21-year-old American who had trekked East to study Buddhism. Her bikini-clad corpse was found on a Thai beach after Sobhraj drugged and drowned her for her travellers’ cheques. How must her family feel, seeing a fictional version of her laughing, wide-eyed, on a night out in Bangkok’s strip clubs, before finding herself paralysed and terrified in the back of Sobhraj’s car on the way to the coast?

Talking to me from the Bloomsbury home she shares with her brother, Lucas, Bamber admits the story is “shocking… so murky and sinister you couldn’t make it up”. But she argues that The Serpent’s treatment “is really not gratuitous”. “The BBC and production team went to great lengths to reach out to all the victims and the victims’ families so as to be respectful,” says Bamber, who herself got in touch with the real Angela Knippenberg. “She’s fiercely intelligent and still working at the UN in peace and disarmament,” explains Bamber. “She told me that when she and Herman heard there was nobody else looking for these lost young people, then there was no question in their minds. She said: ‘We knew we had to do it. It was a moral imperative.’ ”

When she asked Angela if she had ever been scared of Sobhraj, her reply was that “she was mostly scared of Herman losing himself in his obsessive hunt for the killer”. “You’ll see that, in the series, most of the characters lose a bit of themselves to Sobhraj,” says Bamber. “He got under people’s skins. Angela was scared that Herman would self-destruct in his mission for justice. Angela is the only character who didn’t lose herself. And it’s the morality of the Knippenbergs that The Serpent celebrates. Not the coldness of the killer.”

With her Victorian doll’s face and wide, blue, Alice-in-Wonderland eyes, Bamber radiates a vintage ideal of virtue that has seen her cast in a long line of good girl roles. The youngest ever member of the London Players’ Theatre, she has been a professional actor since the age of 13, when Sir Trevor Nunn picked her to play Young Jenny in Andrew Lloyd Webber’s Aspects of Love at the Menier Chocolate Factory. “My dad’s in finance and my mum is my manager,” says Surrey-born Bamber, “so I’m not sure where the acting gene comes from! I was the kind of kid who spent a lot of time skateboarding down country lanes… although I’m really clumsy, so there were a lot of bruises!”

She quickly moved on to TV and film work, handling martial arts in a corset to play Lydia Bennett in the 2016 film Pride and Prejudice and Zombies and nailing a Texan twang as Jake Gyllenhaal and Isla Fisher’s daughter in Tom Ford’s chic thriller Nocturnal Animals (2016). Last year, she appeared on the small screen in Les Misérables, with Dominic West, and as nightclub dancer Mandy Rice-Davies in the BBC’s six-part series The Trial of Christine Keeler.

The latter, written by Amanda Coe, retold the 1961 Profumo Affair through the eyes of the two complex women often – untruthfully – dismissed as “harlots” and “call girls”. While the more vulnerable Keeler was damaged by her sudden infamy, the beehived and “ballsy” Rice-Davies made hay. Bamber loved playing her at the Old Bailey, blowing kisses to the press in her flamingo-pink hat and delivering her famous line from the witness box: “Well, he would, wouldn’t he?” in response to Lord Astor’s claim that he had never met her.

Today, Bamber tells me she is “inspired” by the “hard-working and ambitious” Rice-Davis, and her role in changing Britain’s view of female sexuality. “Mandy and Christine were two young women who were just enjoying themselves in a world a lot of women like them never got to see. It was a time when women were starting to enjoy sex and not feel shame about that. Putting them on public trial in that way was just awful, but Mandy handled it with strength, savviness and sophistication. She span it around and said: ‘You guys just f----- up my life, so I’m going to use [the fame] to my advantage.’ She became a millionaire in the end. She really turned it around!”

Even so, Bamber knows women are still judged more harshly than men on their private lives, and she will not comment on her own. She finds walking red carpets as herself “really scary” and won’t discuss the two-year relationship with Bodyguard star Richard Madden she is reported to have ended last year. And she won’t comment on the scandal surrounding her “amazing” Les Mis co-star West.

In 2019, the married, 50-year-old West said women “should be more indulgent of affairs”, before being photographed this year snuggling up to actress Lily James on a scooter while filming in Rome. Bamber says that she’d “love to sit down with a glass of wine” with me and work out whether charming men can still get away with bad behaviour more easily than women, but that it’s too big a question for our interview.

“But,” she relents, “I think people nowadays are being held accountable more often for their actions and I’d like to think that my generation have something to do with that! Proud!”

Bamber also tells me she has been “doing some thinking” about the violence against women we’ve been seeing on screen, particularly since accepting the role of a gang-rape victim in the forthcoming film The Seven Sorrows of Mary. She’s said that when she finished shooting the scenes during which she was assaulted in a van, she asked if she could set fire to the vehicle.

She perks up when I ask about being a “brand ambassador” for Chanel. “As an actor, I’ve always been inspired by the way clothing and make-up transforms people.” Her visits to the Chanel archive have “impregnated my acting in so many ways,” she says. “We were talking about which perfume a character would use on set once and I could instantly show them a 1920s bottle. It’s those little details that make up the art.”

By a strange coincidence, it was a perfume bottle that Sobhraj used to escape from a high-security Greek prison in 1975. Having inveigled his way into the prison hospital by swallowing some of his own blood and spitting it out for the guards, he stole a bottle of scent to light a fire in the van in which he was being transported. He was jailed again in 1976, then in 2003 received a life sentence (largely thanks to Knippenberg’s diligently photocopied evidence).

Basking in his notoriety, Sobhraj liked to say that killers “either have too much feeling and they cannot control themselves, or they have no feelings. It is one of the two.” He never said which category he fitted into. Viewers of The Serpent will have to make up their own minds.

The Serpent starts on BBC One at 9pm on New Year's Day. The full series is on bbc.co.uk/iplayer