She seems like an enthusiastic teenager – albeit a whip-smart one – talking about a latest creative project, but underneath her tousled blonde hair lies a brain and a talent which has seen her reaching towards the top of her profession.

Later, in the rehearsal room, a member of NBT's marketing staff sits with me as I watch Marston put her dancers through their paces. My contact, who saw Marston as a performer, sighs as we watch her at work and says: "she was such a beautiful dancer".

Before going into rehearsals, over the course of an hour, Marston's unguarded nature is refreshing. She will happily discuss the criticism levelled at the company she has been employed to work for, talk about her attitude towards turning a Dickens classic into a dance piece, speak with uncensored pride about her achievements and even give away her methods of choreography.

The choreographer, who has already achieved much in her dance career, is the first person to be brought into Northern Ballet Theatre to create a new piece under the tenure of artistic director David Nixon. Since he arrived in 2001, Nixon has occasionally brought in other works by different choreographers to complement the ballets he himself creates, but this is the first time he has effectively handed the company over to someone else.

"If I'm honest, I'm not exactly sure why; you'd have to ask him," says Marston."But he seems to be happy to leave me alone to get on with things." Classically trained at the Royal Ballet School, at first glance Marston does not seem like an ideal fit with NBT.

The company is increasingly known for straying away from the constraints of classical ballet and concentrating on strengthening the narrative. The assumption is that Martson's training at the Royal Ballet would make her baulk at the ideas introduced to NBT by David Nixon.

While her career began in classical ballet, Marston soon moved on to work with contemporary dance companies, a move which reflected her own personal tastes and makes her a natural collaborator with the company. "One of my regrets is that I never came here as a dancer," says Marston. "You get a real sense that it's like being a part of one of the old fashioned troupes that used to exist. The dancers are allowed to bring their own personalities into the work, they're not just there to perform the technique."

Those personalities are going to be key if Marston is to make a success of this latest project. Having danced in Europe for much of her career, Marston returned to London in 2000 to pursue her career as a choreographer.

In 2002 she created Facing Viv for the English National Ballet, a piece based on TS Eliot's relationship with his first wife. The piece brought her high praise and also brought her to the attention of Nixon. This led, in 2004, to Cathy being invited to bring a piece to NBT to be performed as part of a triple bill. A desire to make something edgy and abstract created Dividing Silence. A year later Marston scored a major hit with Ghosts, Ibsen's masterpiece, at the Royal Opera House. After seeing the piece, Nixon decided Marston was ready.

She says: "I think he knew exactly what he was doing with me. He was waiting for me to be at the right point in my career to be able to take on a challenge like this."

And what a challenge.

Marston is turning Charles Dickens' historical novel A Tale of Two Cities, into a piece of dance. When she suggested the dance piece to Nixon, her memory of the story was as a film version she saw as a child.

"What I remember very vividly is the love story that was at its heart," says Marston. "I was a romantic even then and I remember the story of these two men who love the same woman, this girl who seems condemned to die and that last speech by Sydney Carton. That was enough for me to want to do it as a dance piece." She suggested the idea to Nixon who immediately came on board and Marston began planning the piece. She knew the key lay in reducing it to its essence. Remembering the story that gripped her as a little girl, this meant finding the love story at the heart of the book. "I could never say we've improved on the story, but we've taken out a lot of the court scenes at the beginning of the book and Lucie has become more of a three-dimensional character," says Marston.

"In the book it is difficult to get a sense of her as a real person, there's no sense of her sexuality or her desires and that was something I wanted to explore."

NBT was not universally praised for its last project, which saw Nixon turn Hamlet into a ballet.

Marston says that mainland Europe consider the British critics a strange set of beasts, unwilling to view dance outside of certain parameters and that NBT's pushing at those parameters is the reason why it attracts sometimes negative reviews. It is not something which concerns Marston, who clearly feels a responsibility to the author, her audience and to the dance. "This is a piece which I have created using the Dickens story as an inspiration – and hopefully I have done it justice."

Northern Ballet Theatre's A Tale of Two Cities premieres at West Yorkshire Playhouse, Leeds tomorrow.

CATHY MARSTON'S CV

1976: Born in Newcastle upon Tyne.

1992: Joined the Royal Ballet Upper School.

1993: Joined the Zurich Ballet.

1996: Joined Luzern Ballet and later spent a year with the Bern Ballet.

2000: Returned to London to work as a freelance choreographer/dancer.

2000: Shortlisted for the Jerwood Choreographic Awards.

2002: Made the first Associate Artist of The Royal Opera House.

2003-04: Shortlisted for UK Critics Circles Awards

2004: Choreographs Ghosts, based on Ibsen's play.

2004: Commissioned to create four short works for Channel Four.

2006: Formed her own company which toured the UK.

2007: Appointed director of the Bern Ballet, Switzerland.

WHY I LET CATHY TAKE OVER MY COMPANY

David Nixon has taken a big step in essentially handing over his company to another choreographer. Here he talks about his thoughts.

"The dancers are in the best form of the history of the company, producing extraordinary work and performances. Working with Cathy has been a marvellous journey and the resultant A Tale of Two Cities is a beautifully crafted and moving new narrative work.

It is a compliment to the creative team and NBT company. It has been particularly exciting for me as a director to step back and watch the process and work as a ballet master. To see a different approach and to understand more succinctly the beauty of narrative dance from the outside in.

It is my impression that an audience limits its exposure to new narratives because it expects the work to relate too closely to the source and is either turned off because they do not like the title or are disappointed because they expect a replica.

A dance narrative is inspired by the source but offers a new perspective, while simultaneously offering an alternative engagement because of the visual and physical language.

We can see at once the essence of Dickens but also the beauty and expression of movement through space to music which tells its own tale.

The creation of new narrative work is at the heart of NBT's artistic mission and is key to our unique identity.

Always an exciting time, it is of particular interest this season as the very talented Cathy Marston does her largest work to date and first full evening work for us.

Cathy is a gifted story-teller and inventive choreographer, and her chemistry with the company has resulted in a wonderful new telling of Dickens's famous story.