The English actress plays the real-life girlfriend and accomplice of 1970s serial killer Charles Sobhraj.
Time to say bonjour to another creepy serial killer.
ENTERTAINMENT WEEKLY:What was your reaction when this part came your way?

Roland Neveu/Netflix
The psychology of her felt really original and like someone I’d never played and really something to explore.
So, I’m assuming there was a vocal coach or language coach at your disposal?
So he was teaching me English-French, but also French in the French accent and French-Canadian.

Roland Neveu/Netflix
It was a really quick process, actually.
I had about three to four weeks [to master the language and accent].
That’s so little time!

Roland Neveu/Netflix
Did you learn it phonetically or did you understand everything you were saying as you said it?
How can I describe it?
It was like a trifle, layer upon layer upon layer.
I’ve never quite described it as a trifle before.
Would you stay in the language or even just the accent between takes?
On set, generally, I stayed somewhere in-between just because the mouth placement is so different.
That’s so impressive though.
There was something about her, visually.
I realized she lives in such delusion; she fabricates her own world to exist in.
It was all about suppression and how that rises to the surface and gets her.
Did you feel sorry for her at times?
Yeah, I went between all things and I still do.
That’s what was so confusing about it.
I get asked a lot, is she a victim or is she not?
She is and she isn’t.
It’s both because she actively went after Charles.
There’s a certain level that she chose.
It’s not simple.
Did you get to meet any of the real-life people the characters are based on?
Yeah, we did!
They came to set, quite a few of them.
The real Nadine [Gires] came to set and Herman Knippenberg helped with a lot of the research.
She told me a really interesting thing.
I asked her if they were really in love.
She said she thinks so at a certain point, but then he was incredibly unfaithful.
They would be a monster."
That isn’t an innocent woman who doesn’t know that he’s got the devil in him.
Tahar is so good at playing Charles.
He’s almost effortlessly sinister.
I’m assuming he’s a lot nicer in real life though.
How was working with him?
You launch straight into a job and you never know what to expect.
I was a real fan of his from when I went to the London film festival whenA Profitaired.
It was so easy.
I feel like our instincts are completely the same.
We didn’t really have to over-discuss anything.
I felt very safe with him.
He really pushes you and challenges you as well.
He’s full of surprises and a very dynamic actor.
Our director, Tom [Shankland] as well, is just the coolest guy.
Tahar’s become a very close person.
We just explored it together.
It was a real, amazing partnership.
I can’t not ask about the ’70s fashion.
How much fun was that and did the clothes and the wigs help with getting into character?
I was part wig.
[Costume designer] Rachel Walsh was looking at those images, which are great.
The Serpentarrives Friday on Netflix.