As the series goes on, we learn more about Kay and why she makes the choices that she makes. “She’s not very proud of her upbringing or background, and it’s turned her into an opportunistic person. But a very modern woman for that time period, especially in how outwardly confident she is. From the way she talks to the way she dresses, Kay commands attention and wants to be seen and heard in every room she’s in,” says Keene.

It’s what the actor loved about the character and made her a lot of fun to play. “I do feel she stands out in a way that wasn’t the done thing at the time and I love that about Kay.”

Hyland also admires this about Kay and explains how Audrey is a very different kind of woman who is likely intimidated by Kay’s confidence and modernity. “For Audrey, it’s almost a jealousy of Kay’s perceived freedom and independence and perhaps even an element of lust for a life that you desire. It’s similar to that feeling you get when you’re not sure if you want to be her or be with her,” says Hyland.

And here’s one particular scene that both actors loved a great deal that really highlights this dynamic between the two women and it’s a dancing sequence during one of their evenings at Gull’s Point. Kay is the type of person to put on a record and just get up and dance in a room full of people, but Audrey is much more controlled – even if she wanted to dance, she wouldn’t because of what people may think of her.

But when Kay offers her hand to Audrey and invites her to dance with her, there’s a brief will-they-won’t-they moment before Audrey does choose to dance with her ex-husband’s wife. “It’s always interesting to have your character do something that just isn’t part of their personality, that the viewer wouldn’t imagine her doing,” adds Hyland. The dancing scene is such a brilliant depiction of Kay realising she’s part of Nevile and Audrey’s strange little game and deciding to play too. “Do they hate each other? Are they going to fight? Or will they kiss instead? This scene is the epitome of the relationship between the two of them,” says Keene.

As well as the gripping murder mystery storyline, it’s the complicated relationship between these two women that really makes the show what it is. The cold stares, the quick sharp looks over the shoulder and the cutting quips between Audrey and Kay not only make for brilliant and dramatic television, but they also centre the wants and needs of women at a time when these things were rarely taken into consideration.

Agatha Christie’s Towards Zero will be available in full on BBC iPlayer from 6am on Sunday 2 March, with episodes airing weekly on BBC One from 9pm that night.

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