Hit Play above to watch Josh Hartnett and The Fear Index cast talk book to TV adaptation

Robert Harris is the talk of TV town at the moment, as two of his books are being adapted for the small screen within a matter of weeks of each other.

Munich: The Edge of War was released as a film on Netflix at the end of January, while four-part TV series The Fear Index is released on Sky Atlantic and NOW on 10 February.

Based on Harris' 2011 novel of the same name, The Fear Index is a psychological thriller starring Josh Hartnett, Arsher Ali, Leila Farzad and Gregory Montel.

It delves into the murky world of financial markets and dangerous conspiracies, and stars Hollywood actor Hartnett in the lead role of Dr Alex Hoffman - a genius computer scientist who's created AI-driven software that exploits fear in the financial markets.

Speaking exclusively to BT.com, the cast talk about starring in the series, including what they took from the book, the changes they made to their characters, and much more...

1. Reading Robert Harris’ thriller as research

The Fear Index key art

In 2011, when The Fear Index was published in book form, there was some talk around it being adapted into a film. More than a decade on, the adaptation of Robert Harris' novel has finally arrived in the form of a thrilling, four-part TV series.

The longer format allows for more detail, but adapting a 400-page book into a different medium will naturally mean there are still some constraints, with sections cut out or glossed over for TV. That’s why all the cast delved deeper into the original source material, to better understand the story of The Fear Index.

Josh Hartnett (Pearl Harbor, 40 Days and 40 Nights) plays the lead character of Dr Alex Hoffman - the focal point of the show. When his character endures the worst 24 hours of his life, he is forced to question everything he sees with his own eyes. 

Hartnett praises Harris - whose writing penchant is historical fiction - for making fictional stories such as The Fear Index seem incredibly relevant. He tells BT.com enthusiastically: “The book is amazing. I think that’s the reason we all signed onto the show. I know it’s the reason I signed up! 

“I didn’t realise how much of a Robert Harris fan I was until I read the book. It just has a sensibility that it’s not just a fiction writer trying to write an interesting story about our time. He’s writing something that seems to be a historical artefact of the time.”

Arsher Ali (Line of Duty, The Informer) plays Hoffman’s best friend and business partner, Hugo Quarry. He says studying Harris’ book before filming allowed him to have a deeper understanding of the friendship between the two characters.

“I think there’s a lot of backstory in the book that was worth keeping in mind, because we don’t get to explore that in the show,” he explains to BT.com. "Some of that stuff was really useful, especially about how they met. We don’t really touch on how that, but - because they’re complete opposites - you kind of want to know about that.”

BAFTA-nominated actress Leila Farzad, who you might recognise from her role in I Hate Suzie alongside Billie Piper, plays Gabby Hoffman in the series. Gabby is the wife of Dr Alex Hoffman, and begins to lose her patience when her husband's sanity is questioned.

Farzad says she was something of a Robert Harris superfan before signing up for the project: “I read the book before I read the script. Part of the reason I said ‘yes’ was because I thought it was a great book. It’s Robert Harris, and he’s just a bit of a genius!"

She adds: "Also,  [part of the reason I signed up for The Fear Index was because] I’d never done anything like it. I’d never done a psychological thriller. It had an international feel, with an international cast."

2. Adapting the central characters for TV

The Fear Index Arsher Ali

The cast had their pick of research material to get their teeth into for The Fear Index in the shapes of a comprehensive novel as well as an expertly adapted script. But they also brought their own suggestions to the table when it came to adapting their characters for television.

Farzad, for example, was conscious of making her character more rounded, and actually suggested making Gabby bilingual. Explaining the conversations she had about her character, she tells BT.com: “I had some conversations with the writers and the directors of the show, and we tried to mould her into a more three-dimensional character.

"I was very aware that Gabby could have been a ‘Where are we going? What does this mean? Who is that?’ wife. We had a chat about trying to make her more rounded, especially because of the fact she’s super bright. I asked if we could make her bilingual, because I don’t think she’s bilingual in the book. They said ‘Yes’.”

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Speaking of being able to speak multiple languages, Hartnett reveals that Hoffman is trilingual - he just never speaks in any language other than English. But, rather than changing specific elements of Hoffman’s character from the book, he found his character’s monologues in the book particularly useful for getting into character.

He says: “The book just had so much more internal monologue that was so subjectively written than the show could be, that I had a lot of internal dialogue from the character already about each scene, which was great. Everything I needed for the character was in the book. 

“There were lots of times on set… where we’d take some dialogue from the actual book, and bring that to the dialogue. Sometimes that worked very well, even if it wasn’t written into the actual scene.”

Arsher Ali adds: "I’m just like Hugo is in the book in some ways, but in some ways the character is having to fight for his place at the table, against other forces who want to keep him down which is he why strikes out on his own."

3. A work of fiction - but frighteningly real?

The Fear Index Josh Hartnett

The critics’ response to the novel at the time of publication in 2011 was that it was 'of the moment’ and ‘so up to date it could have been written next week’.

Fast forward a decade, and it couldn’t be more topical, as the worlds of politics, technology, finance and fear interwine. As Hartnett explains, if an author was to write about today’s socio-economic climate, The Fear Index would be the story.

“I feel like [Harris’] understanding and interest in the society that creates this story, as opposed to the story itself, was what made this so appealing to me," he says.

"What is it that he could write about our times, that’s batsh*t crazy? This is it.

“The interaction between technology, finance, science and totally unchecked power. That’s what you want to write about, if you’re talking about this time. I think he does it really well.”

French actor Gregory Montel (Call My Agent), plays Detective Jean-Philippe Leclerc in the show. He agrees that Harris’ book is more of a social commentary than a work of fiction.

He tells BT.com: “I really feel that the book was more political because it’s a huge story about more than fear. I think that there is something more social in the book.”

Farzad concurs that the world of The Fear Index, where Hoffman creates a new AI system which is designed to operate faster than human beings, but which then becomes bigger and more dangerous than him, is entirely plausible. 

“I think it’s even more possible now than when he wrote it,” she says. “It’s an almost Frankenstein story about creating something that is eventually going to come back and try and destroy you.”

Montel adds, rather pessimistically: “I think this could be a real story. I think that AI is everywhere now, and it’s so important. We just have to find the brain to do that. Robert Harris wrote this famous brain [in Dr Alex Hoffman], now we just need to find the brain that could do that in real life... The real fear is here.”

Watch The Fear Index on Sky Atlantic with a NOW Entertainment Membership from Thursday 10 February.