New Channel 5 thriller The Au Pair sees the return of Sir David Suchet to the small screen after a gap of almost seven years.

After a few years working on the stage (save for a voice-only role in His Dark Materials), the RTS award-winning actor was pleased to be back – and, unlike his most famous TV role, Hercule Poirot, “playing English, which was nice”.

Suchet is George, a diabetic grandfather keeping a terrible secret: “What fascinated me, and made it different, was something that I first tapped into when I did [on stage] Arthur Miller’s great play All My Sons, where I played a man who did the wrong thing for the right reasons.”

In the four-part Channel 5 show, the au pair of the title infiltrates an apparently blissful Cotswolds family home and mayhem ensues.

The Au Pair is made by Anglo-French factual producer Pernel Media and Irish company MK1 Studios, in association with ITV Studios (worldwide distribution) and Canal+ (France).

Executive producer and Pernel founder Samuel Kissous was visibly thrilled in discussing Pernel Media’s first English-speaking drama series. “In France, we have an expression that says, ‘They didn’t know it was impossible, so they made it.’ It did feel like an impossible task at first. And then somehow it happened, so there is still magic in television.”

Pernel has made factual shows for Channel 5 over the past decade, which led to a chat between Kissous and the channel’s Deputy Chief Content Officer, Sebastian Cardwell, about making “a story that brings together elements from France and the UK”, recalled Kissous. He was speaking with the cast and director following the premiere of the drama’s first episode in central London.

The Au Pair is a departure for Sally Bretton (persecuted stepmother Zoe Dalton and George’s daughter), best known as Lee Mack’s wife in long-running BBC sitcom Not Going Out. “I haven’t done anything like [this] before,” she said. “This was a real dash at something very dramatic.”

Vera’s Kenny Doughty (DS Aiden Healy in the ITV series) plays Zoe’s doctor husband and was gripped by the script. “I’m a fan of late-80s/early-90s thrillers like The Hand That Rocks the Cradle, Fatal Attraction and Basic Instinct. I’m also a sucker for guilty, binge-reading pleasures. The script was a real page-turner,” he said.

Discussing the plot twists, Doughty added, to much audience laughter: “After years of being a detective, I still couldn’t work it out.”

French actor Ludmilla Makowski (Netflix series Lupin) plays the avenging au pair, Sandrine. Though admitting to finding working in a foreign language a “big, big challenge”, she jumped at the chance to appear in a UK drama. “It was a dream come true. Every actor in France has the ‘American dream’.… movies [and TV] in the UK and America are bigger, and we want to be in them.”

She added: “For every actor, it’s a dream to play the villain because we want to play someone that we’re not – it’s more interesting.”

The drama was shot in the Republic of Ireland, doubling for the Cotswolds, and it looks beautiful, replete with bright, summer colour and a striking contrast to the murky secrets of the Dalton family.

Director Oonagh Kearney (Channel 4’s Vardy v Rooney: A Courtroom Drama) said: “If you think about the colours in the [family’s] garden, just below the [flowers] you look down into the earth and the roots of the family’s story are dark, with a lot of dark secrets that get unravelled,” she said.

“We wanted to invite the audience to enjoy the villainy of Sandrine – and she does it with such va-va-voom – while at the same time not shying away from some of the more serious themes in it, which [include] the importance of family.

“Within the thriller genre, all of us were working hard to give the characters authentic stories and arcs.”

The Channel 5/RTS London event was hosted by the journalist Caroline Frost at Picturehouse Central in central London. It was produced by Ian Johnson and Phil Barnes.