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"Chris is the father of Amelia [Genevieve Barr], a deaf teenager, who has recently had a cochlear implant. He had always accepted in his eyes the terms of her deafness, whereas his wife Anne [Gina McKee] has been far more active in pursuing her goal to allow Amelia to have access to the hearing world, as advances in science allow.

"Chris's attitude is much more 'live and let live' and let Amelia cope with life as it is. Anne puts pressure on her to be more 'normal' so, of course, there is tension.

"And then, when Amelia finds herself involved in this murder, it brings to surface all these emotions that have been simmering underneath – pressures that the story brings to bear on them all.

"The theme that bubbles under the main story is that, of course, you want the best for your child: but is the best for your child to accept them as they are, or to conform to other people's idea of what is normal?

"When under the microscope, this story becomes quite a pressure cooker. Add into the mix Amelia herself, who has her own view on the situation, fluctuating between wanting to stay in the silent world or entering the hearing world, but she wants to find her own terms.

"Both parents are trying to do the best for her and what they were trying to do was ease her path of growing up and becoming a woman. If she hadn't witnessed what she witnessed, it might have been a different path – careful what you wish for as it comes back to haunt them in different way...

"Gina [McKee] and I have worked together loads of times, we've known each other for over 25 years. We met at the National Youth Theatre in our teens, so we have a nice shorthand – basically I just do everything she tells me to do! We've played star-crossed lovers or ships that pass in night but have never played husband and wife. We had our first bed scene the other night which went as far as holding hands – a bit like going to bed with your sister!

"Genevieve [Barr] has been on a steep learning curve. She is very instinctive and stands her ground and asks all the right questions. She's taken to acting like a duck to water and the hearing impediment hasn't been an issue at all. She knows the script better than anyone else, feeding me my lines! She's a natural and strikes me like she's been doing it for years.

"Playing a father of a deaf child, one suddenly sees all the paraphernalia and equipment needed, from the smallest things like the front door bell, an alarm clock – things that one takes for granted you become aware of. This story is challenging enough for any parent to get their head around but [for Anne and Chris], as parents of a child with different abilities, just amplifies it even more and makes the stakes even higher. It accentuates everything even more when your child is even more vulnerable.

"I'm playing Chris with a Scottish accent, as I'm playing Dougie's [Henshall] brother. All slightly surreal, as the story is set in Bristol, with two Scottish brothers and we're filming in Ireland with Dervla [Kirwan] who's Irish and Gina [McKee] who is a Geordie – a right hotchpotch!

"Dougie and I have worked together before and I unashamedly have taken a tape recorder to Dougie who has read all my lines and I try and parrot them! I've also spoken on the phone to the lovely Julie Graham, who's been helping me out. I'm one-quarter Irish and one-quarter Welsh, so have played various accents. It's just another part of the job and I don't get too freaked out by it.

"I love different accents but Dougie's is quite specific, from just outside Glasgow. I don't know if it's any good but I'm sure there'll be angry letters from Scotland!"

Hugh Bonneville is currently filming the new series Downton Abbey. An established television, theatre and film actor, recent credits include: Murder On The Orient Express, Lost In Austen, Glorious 39, Ben Hur and, in the theatre, Cloaca at The Old Vic.

He won the 2002 Best Newcomer Award at the Venice Film Festival for his role in Iris.