Doctor Foster hauled in more than 10 million viewers for its series finale, a feat rarely achieved in a world of multi-channels.

But the tale of a woman betrayed by her husband and seeking revenge captured the audience's imagination thanks to its original take on a well-worn plot and pitch-perfect performances.

[Read more: All you need to know about Doctor Foster series 2]

"It has a fantastical, weird sexy edge as well as being deep-rooted in naturalism. It also has an exaggerated way of showing how far you could go if you really wanted to," comments Suranne Jones, who returns to the title role alongside Bertie Carvel as her estranged husband Simon and Tom Taylor as their son, Tom.

Doctor Foster series 2

"She's an everywoman, as in you know her," says Jones of her character's appeal.

"She shops at Reiss, she's attainable yet aspirational, (at least) the life was until it blew up."

Writer Mike Bartlett's returned to pen the second run and recalls watching the end of series one.

"The more I looked at that last scene (when Foster's getting back to normality by attending to someone in the street), the more it looks like a happy ending but there are lots of threads untied and then when it went out people said 'Did Gemma really get justice?'

"What was pleasing about that is it feels like the audience is feeling what I do, that it doesn't end there. There's more to tell so when we had the opportunity I thought we should."

[Read more: Who is Suranne Jones? Surprising facts about the Doctor Foster star]

After Gemma Foster dramatically exposed her husband's betrayals, he left town but at the beginning of series two, Gemma's life is destabilised when he, Kate (the woman he left her for, played by Jodie Comer) and their child return.

Doctor Foster series 2

"Everyone has had a relationship, has an ex-partner," notes Jones, 39, who's married to magazine editor Laurence Akers.

"We all know what it feels like to be in a room with an ex-partner. All those thoughts and feelings you have when you've been in a relationship. It's the discomfort of not being in a relationship when an ex-partner is or the thoughts you have that you don't speak about. Hopefully men and women will recognise some of themselves in our story."

In one of the many tense conversations between Gemma and Simon during episode one, he tells her she hasn't moved on and that she even wears the same clothes.

[Read more: Doctor Foster series 2 - Meet the cast and characters]

"It was really interesting when we were thinking about the look for Gemma, we knew it was two years later so we gave her a new look," notes Jones who has also starred in Coronation Street, Scott And Bailey and A Touch Of Cloth.

Doctor Foster series 2

"I was so convinced, I said 'You would, you'd change, you'd move on, you'd attempt to be different' and then when we saw it in the screen test, every single one of us went 'No, she's moved on but actually she's comfortable with her bob and her work'.

"She's put up her walls and she would've been confident and comfortable in that life living with her son and getting him to 18 and moving out but he (Simon) moved back. So actually, it was the right decision to move her on but leave her embalmed in a way."

We also see Gemma reluctantly accept a date, which ends in unexpected fashion.

"The thing that interested me is that when people talk about someone moving on, especially with a woman, it invariably means finding someone else," comments Bartlett.

"Do you find a replica of the person you had before? What are you looking for? Do you change your taste? It occurred to me I'm not sure Gemma really knows what she's looking for and what her taste is but certainly in episode one, it's all activated by the arrival of Simon. I think that's crucial. She wouldn't have gone on a date normally but it's having to avoid the (Simon and Kate) wedding party that means she goes on that date.

Doctor Foster series 2

"So she's already starting to change herself because of the arrival of Simon, which means everything in her life is centring around this one person who she hates most in the entire world. It's that contradiction which I think is at the heart of this series."

If you thought series one was tense, prepare yourselves as these next five episodes are set to get even darker.

But while Simon became one of the nation's most disliked characters, Jones feels Gemma is equally flawed.

"They can (both) be unlikable people and what betrayal does to a person can make them ugly. Gemma doesn't behave well. Before she did that through hurt and now she's channelling her anger, it becomes dark and twisted."

Since series one, Jones has won a TV Bafta and a National Television Award for her memorable performance. She's also become a mum for the first time.

Doctor Foster series 2

"I could've played a mother without being a mother. I have played mothers without being a mother but I think what it (motherhood) did do, is make me realise the gravitas of that unit falling apart because I'd go home at night and I'd have a baby to put to bed," says the actress, who hails from Oldham in Greater Manchester.

"I think it definitely made me realise when two people get together and have a child out of love and then they split, what it is to parent a child and be in each other's lives when you are damaged and hurt without damaging and hurting a child? It certainly made me more aware of that."

Asked if they'll be back for a third series, Bartlett ambiguously, and a little ominously, says: "It depends on what happens in this series really." But then this is the man who prefers to keep people on their toes.

Doctor Foster returns to BBC One on Tuesday September 5.

Catch up on series 1 now on BT TV, via the BBC iPlayer app. 

[Read more: Who is Jodie Comer? All you need to know about the Doctor Foster star]

[Read more: Who is Bertie Carvel? All you need to know about the Doctor Foster star]