What happens if pretending to be someone else becomes your entire life?

It is a question at the heart of many of the biggest spy dramas, from Slow Horses to Black Doves - and it is one that TV thriller series The Agency explores more deeply than most.

Returning for a second season, the Paramount+ thriller follows CIA operatives living under deep-cover identities.

It examines not just the dangers of espionage, but the psychological cost of maintaining a lie for years.

Starring Michael Fassbender, Richard Gere and Katherine Waterston, the series is based on acclaimed French drama The Bureau.

The Agency's stars say its appeal lies not in explosions or gadgets, but in the exploration of the moral compromises that come with a life built on deception.

"What sets it apart is that it leans more into the John le Carré experience - the isolation, the loneliness and the reality of the world," Fassbender tells the BBC.

He plays Martian, a veteran CIA operative whose years undercover have left their mark.

The emphasis on character over action divided critics when the first season premiered - some praised its "intelligence and realism", while others found its measured pace challenging.

The New York Times said the show gives "viewers a real taste of what it's like to love a liar", as "we're never quite sure what Martian's angle is, how much of his seemingly vulnerable moments are all part of the game".

That measured pace is something Fassbender believes sets the series apart as it's "steeped in the reality of what this world is".

"Watching the first season is a slow burn - things start to reveal themselves slowly and you're getting introduced to different characters and then eventually they start to intertwine.

"And that's the reality of it, it's not big explosions or set pieces, although there's a bit more of that in season two, it's more about the quiet anxiety and tension because there's a lot at stake."

The German-Irish actor says audiences remain intrigued by spy thrillers because of what it reveals about the people involved.

"People are fascinated by the kind of people that go into this line of work and what kind of people come out of it at the end."

"You see in the show what Martian is like 20 years down the line, compared to someone who is just starting," he says. "Martian was once idealistic and full of hope, then his moral compass gets eroded by the things he has to do and the sacrifices that go into it."

Katherine Waterston, who plays Naomi, a CIA operations officer and Martian's former handler, says The Agency reflects broader questions about trust and truth in our daily life.

"We are in a quagmire, and even when something feels real, you have to be suspicious of it," she says.

She thinks those questions have become even more pressing as AI becomes increasingly embedded in everyday life.

"It's a weird time to be alive as everyone is trying to figure these things out," she adds. "I don't think AI bodes well for society and I think the worst is yet to come."

Waterston also believes greater safeguards are needed around the technology.

"Everything else we consume is regulated, so why do we have a Wild West when it comes to AI?" she says.

"It doesn't need to be in all of our hands for it to do wonderful things."

He thinks that in the wrong hands AI can have a devastating effect on us.

"The people developing it don't even know the full potential of it and that's scary."

He also believes that the rise of misinformation and AI has made the themes of The Agency feel more relevant.

"The nature of trust has changed - there are a lot of stories and theories in front of people and it's hard to decipher one thing from the next," he says.

The actor admits to having found himself caught out by misinformation online, which was spotted by his wife, Oscar-winning actress Alicia Vikander.

"I'll say to my wife, 'Did you see this thing happen?' and Alicia is great because she'll say, 'Where did this come from?' and then I'm there doing due process and fact-checking."

'We'd be awful spies'

Fortunately for both actors, portraying a spy is easier than being one and they say their own jobs are far less demanding - though not without challenges.

Fassbender says his biggest challenge is balancing work and family life.

"The hours are long. I feel blessed and lucky to be doing something I love, but how do you fit in enough time for your family?"

Waterston adds that "it's much harder not to be working than it is to be working as an actor" and she's often annoyed by the idea "that you can seem more deserving of a prize if you say a role was difficult to shake off".

Would they make good spies themselves?

"Terrible," laughs Waterston. "The whole cast has come to that conclusion."

Fassbender agrees, because he feels the personal sacrifices would be too great.

"It's nearly impossible to have a real and balanced relationship."

That's something he came to appreciate while researching the undercover operatives known as "legends", who inspire aspects of The Agency.

"What surprised me was how much it takes out of a person," he says. "Once you've created that legend, you'll never get rid of that personality. You'll lose your own personality in that."

The Agency season 2 is available to watch from 21 June on Paramount+.