Joanne Froggatt and Ioan Gruffudd's dark new ITV drama Liar is destined to get the nation talking.

The story of one night and two very different stories, the series will keep viewers guessing about who is telling the truth - teacher Laura Nielson (Froggatt) or surgeon Andrew Earlham (Gruffudd).

[Liar episode 5 review - Thriller takes even darker twist]

Keep reading for a quick guide of the key cast and characters in the series.

[Read more: All you need to know about ITV's dark drama Liar] 

Laura Nielson (Joanne Froggatt)

Liar - Joanne Froggatt

Intelligent, outspoken and strong-willed, Laura is popular with both pupils and staff at the local secondary school where she teaches English. When we first meet Laura, her ex-boyfriend Tom has just moved out and she is starting life again as a single woman.

Andrew Earlham, a handsome father of one of her pupils, takes an interest in her and asks her out. The date goes well, the
chemistry between them is electric, but Laura cannot predict how this single encounter will unravel her entire life, pitting the two against one another in a brutal battle for the truth.

[Read more: Joanne Froggatt has reservations about rape drama Liar]

What makes Liar such a compelling story?

When I read the script it was just such a page-turner. It’s a compelling story because of Jack and Harry’s writing. It’s a psychological thriller with a real intelligence about it, and when I read the script, it brought up a lot of questions about all sorts of subject matters and how we, as a society, think about certain things.

How difficult it is to know the truth at times whatever the situation may be, and it also has an element of who is really trustworthy in your life, and at what point do you decide to trust someone. You may find things out about someone that you never expected, whether you have known them for many years, or whether you have known them for five minutes, so it brings up lots of interesting questions.

What are the key themes of the series?

The key themes for Liar are, as the title suggests, lies and secrets, but also, truth, and how you get to that truth. Do you get to the truth at all costs, or do you get to it through ways that aren’t necessarily morally correct? There is the theme of trust, of non-trust, of obsession, along with someone losing their faith in humanity, to a certain extent. How to cope with your world crashing down around you; how you cope with that and what your choices are to get out of the situation, how to move on in a positive way, and the idea of making the right decisions when you are in that mind frame.

[Read more: Downton to the Royle Family - Joanne Froggatt's best ever roles]

Andrew Earlham (Ioan Gruffudd)

Ioan Gruffudd - Liar

Outwardly charming, Andrew is a well-respected cardiac surgeon, popular with patients and colleagues alike at Broadhill Hospital, where he works.

Recently widowed, Andrew takes an interest in Laura, who teaches his son, Luke, at the local secondary school, and asks her out on a date. The two share what Andrew believes to be a perfect evening, but when Laura’s account of events turns out to be wildly different, he finds his world collapsing around him. Andrew’s perfect life hangs in the balance and he will turn to any means necessary to protect it.

Tell us more about Andrew…

I think Andrew is a very driven character, and what he wants he gets. He uses his charm, intelligence and personality to achieve that. He’s very dedicated to his work, basically a man who has everything. Dresses great and is admired. Ticks all the boxes. We discover that he is a widower, having lost his wife about ten years ago. He’s had to raise his son on his own, they have a
fantastic relationship, he’s done a good job of raising his son, and being motivated by his career. He’s a young consultant, and has dedicated he’s a lot of his life to his work.

On the surface, he’s driven, he’s dogged, he’s determined, but he’s also a fantastically charming guy to be around.

How does he feel about being accused of being a liar?

When Andrew is accused it offends him greatly, his status in the community is very important to him. He’s a very proud of what he has achieved, and I think it shakes him to his core, he’s angry, and he’s shocked. I think one of the driving forces of his anger is the fact that how he is perceived by the world has changed, and I think that really makes him angry.

[Read more: 5 surprising facts about Ioan Gruffudd]

Katy Sutcliffe (Zoe Tapper)

Zoe Tapper

Smart, frank and upbeat, Katy shares many qualities with her sister Laura. The two are very close, and Katy values their friendship above all others. However, when she sets Laura up with Andrew Earlham, she sparks a series of events that threaten to divide the sisters forever. Because Katy is hiding something – a secret she dare not reveal to those closest to her, especially her husband, Liam. If the truth comes out, Katy stands to lose everything.

Tom Bailey (Warren Brown)

Warren Brown  - Liar

Passionate and impulsive, Tom is popular with his friends and on good terms with his ex-girlfriend Laura, but is unlikely to make many allies in his line of work as a local police officer. His quick temper and tendency to bend the rules have always stood in his way, and as he becomes embroiled in Andrew and Laura’s conflict, his tempestuous nature leads him down a dangerous path. Protective of Laura, Tom’s fight for the truth lays bare his own web of lies, and his secret threatens to destroy the ones he loves the most.

Liam Sutcliffe (Ritchie Campbell)

Liam Sutcliffe - Ritchie Campbell

Patient, kind, a loving husband to Katy and devoted father to their two little boys, Liam is the picture of happy family life. But not everything is as it seems.

His wife, Katy, has been acting strangely recently – she seems distant, different somehow. As Liam’s suspicions deepen, he starts to question his own actions and begins to doubt whether he can continue to be a trusting husband and a good man.

DI Vanessa Harmon (Shelley Conn)

Vanessa Harmon - Shelley Conn

Calm, professional and passionate about her work, Detective Inspector Harmon takes pride in the care she puts in to every case she is assigned. She has been careful not to let the demands of the job affect her personally. But it’s tough work and, case by case, it’s starting to wear on her. Tired of seeing the criminals she pursues go free, Vanessa’s weariness with the system begins to have an impact on her judgment. Without realising it, her emotional involvement brings her into dangerous proximity to the very criminals she works so hard to bring to justice.

[Read more: Where is Liar filmed?]

DS Rory Maxwell (Danny Webb)

Liar on ITV

Danny Webb played Mortimer in The Halcyon, and Sydney Garin in SS-GB earlier this year. He starred as Hobb in the TV series Humans and was also part of Brookside in the 1980s.

Luke Earlham (Jamie Flatters)

Liar on ITV

The son of Andrew, who has been brought up alone by his father following the death of his mother over a decade ago. He also has a connection to Laura as he's one of the students in her English class.

Dennis Walters (Peter Davison)

Peter Davison in Liar

A surprise cameo from former Doctor Who star Peter Davison turned the show on its head at the end of last night's episode. His character made a phonecall to Andrew, which revealed that this isn't the first time Laura has accused a man of rape.

"My name is Dennis Walters… I hope you don't mind me calling you out the blue, I want to come see you if possible, it's something I would rather do in person. It's about Laura Nielson, I think I might be able to help you," said Davison's character.

"There's something you need to know, she's done this before, she's lied about something like this. I'll be dammed if I let her ruin someone else's life."

Semer (Chu Omambala)

Semer in ITV's Liar

The character is introduced in episode three when his daughter ends up caught in the middle of Andrew and Laura's storyline. 

Chu is best known for his role in BBC One's Doctors and he was also more recently in Stan Lee's Lucky Man and Houdini and Doyle.

Makeda (Tsion Habte)

Makeda in ITV's Liar

The school girl ends up in the middle of Andrew and Laura's storyline in week three when she has a big secret that is exposed. Will her story help expose the liar?

It is the first TV series for youngster Tsion Habte, but she has previously appeared in the film Foster with Liar co-star Ioan Gruffudd.

Catherine Macauley (Dawn Steele)

Liar Catherine Macauley

Laura heads to Edinbrugh in episode four to look into the past of Andrew and secrets about his relationship with his wife. One character she meets is Catherine Macauley - what will she be able to reveal to Laura?

ITV's Liar airs Mondays at 9pm. Never miss an episode on BT TV - catch up using the ITV Player app.

Photo Credit: ITV Pictures

[Read more: All you need to know about BBC crime drama Rellik]