James Nesbitt as Jackman & Hyde

Timid, sweet-natured Dr Tom Jackman is leading a double life – literally. Unable to stop himself from transforming into a vicious, seductive and demonic alter-ego named Hyde, he has struck a secret bargain with his dark side. They have agreed to co-exist peacefully, taking control of their body at agreed times. But how long will this bizarre truce last?

The dual roles of Jackman/Hyde were tailor-made for James Nesbitt, who's switched effortlessly from light to dark parts throughout his career. Just compare his quirky role in Cold Feet to the haunted undercover copper of Murphy's Law. His talents and charm have certainly taken him a long way since his early years an unknown actor, when he was Jerome Flynn's flatmate and actually answered the Soldier Soldier star's fan mail for him. Now one of telly's biggest names, we wouldn't be surprised if he doesn't have time to read his own letters these days.

Gina Bellman as Claire Jackman

Jackman's deal with Hyde has been partly made to keep his beloved wife Claire safe. But, as Hyde becomes increasingly impatient and powerful, it will fall to Claire to draw upon her reserves of courage and strength to do whatever it takes to protect her family.

Born in New Zealand to Russian and Polish parents, Gina Bellman's background is as exotic as her dark good looks. She started acting at a young age, starring as Richard Gere's daughter in the 1985 film King David. Notoriety came when she bared her body in the raunchy Dennis Potter drama Blackeyes, but Jekyll has apparently been her most exciting role so far – mainly thanks to a certain Mr Nesbitt. "James has changed my whole view of acting," she says. "It's the way he's interested in everyone, from caterer to director. He made us feel part of a whole and not fragmented in our roles."

Denis Lawson as Peter Syme

A successful, vastly intelligent scientist and businessman, Peter Syme has big aspirations in the world of genetic research. He also happens to be Tom Jackman's closest friend and confidante, but he may not be quite as transparent as he seems. While his affection for Tom is without doubt, there's definitely more to Syme than he's letting on.

Denis Lawson's distinctive looks and subtle, measured performances have led to him taking on prominent parts in programmes like Holby City and the recent "soap-style" adaptation of Bleak House. But, depending on your age and/or level of geekery, you may just think of him as Rebel fighter Wedge Antilles from the original Star Wars trilogy. Yet Denis has always been dismissive of the career-making role, even calling Star Wars "childish pap". A view which clearly wasn't shared by his nephew Ewan McGregor.

Michelle Ryan as Katherine Reimer

If you ever had a difficult boss, spare a thought for Katherine Reimer. Dr Jackman's beautiful young assistant, she knows his dreadful secret and is responsible for keeping tabs on Hyde. Despite the dangers, she can't resist such a unique job – and, while she appears to be completely loyal to Jackman, she also seems to be harbouring an agenda of her own.

Joining a theatre company at the precocious age of 10, Michelle Ryan was fuelled by a passion for acting throughout her teens. It paid off spectacularly when she was talent-spotted by the BBC and given the role of troubled teen Zoe on EastEnders. She's since had an even bigger break, landing the title role in the epic US sci-fi series Bionic Woman. It's not all gone her way though – despite auditioning, she failed to land the Bond girl role in Casino Royale. Still, at the rate she's going, we reckon it's only a matter of time before she's riding shotgun in that Aston Martin.

Meera Syal as Miranda Callendar

In the great tradition of film and TV private eyes, detective Callendar is cynical, quick-witted and world-weary. She's also very good at her job – a trait that could land her into trouble as she begins to unravel the truth about Tom Jackman and his connection to a century-old conspiracy. A conspiracy that could be even more dangerous than Hyde himself.

Sketch show Goodness Gracious Me may have made Meera Syal a star, but it was by no means her only foray into pitch-perfect, stereotype-skewering comedy. She co-wrote the screenplay for the 1993 film Bhaji on the Beach, the Brit flick which helped put Asian comedy on the map. She then contributed to the sketch show The Real McCoy, which was the direct inspiration for Goodness Gracious Me. Oh, and she's starred in the adaptation of her own novel, Anita and Me. Talented lass, that Meera.

Fenella Woolgar as Min

A world-class whinger she may be, but Min means the world to detective Miranda Callendar. As well as being her girlfriend, Min is also her trusted work colleague, diligently helping Miranda put the pieces of various puzzles together. Together they make quite a team – which is just as well considering the danger they're about to get into with Dr Tom Jackman.

She's a RADA graduate, she speaks French and Italian fluently, and she can knock out some tunes on the piano and flute. (If it's possible to "knock out" a tune on a flute, that is.) She's Fenella Woolgar, and if the name isn't familiar the face may very well be, as she's been all over the place of late, starring in movies like Vera Drake, Bright Young Things and the more recent St Trinian's. And look out for her in the new series of Doctor Who, where she'll be playing Agatha Christie no less.