I think the pace of Shetland is an issue for Calder because it’s much slower than London and the urban policing she’s used to. Ruth’s a little bit of a lone wolf, she often dances to her own beat. The introduction of Ruth Calder creates a different energy for the original cast members and so we see new and different aspects of their characters, as we get to know DI Calder herself.

The crew were all wild swimming after work and I went along to Meal Beach one night and had a dip with them. I was an absolute wimp about it and took about 20 minutes to get in beyond waist height but it was so lovely. Some young people had a fire going on the beach and the water was so clear. That was really special.I loved it actually but to be honest as soon as I read the first scripts I was like “I’m in!”. The writer [Paul Logue] has given everybody a rounded character even down to the hitmen, Howell [Don Gilét] and Nowak [Arnas Fedaravičius]. Just the nuance and the detail of every character is amazing. When the police discover that Rosemary's boyfriend, Liam Kenmuir, has links to Peter and his hospital pass was also used the night Ellen's body was stolen, Tosh and Calder think they've got their killer. However, it doesn't take long for them to work out that he is covering for Rosemary and she is Peter's pen friend and the mysterious sheep-killer. But did she kill Ellen? Tosh's superpower is her empathy, her ability to connect, her humanity. She has a softness and a kindness that is authentic and that means people trust her and will open up to her. This also allows her to get inside the heads of others, and to understand what might be motivating them and to make sense of their behaviour.

She’s formidable, she’s strong, she’s a woman in a man’s world. Ruth Calder’s built this little barricade around herself - she’s almost like an island herself.Ruth is used to getting things right and this is a complex case which is layered and doesn’t quite go the way she expects it to. There are so many different paths that she ends up going down. At times, Calder almost acts like a big sister to Tosh but that might come across as nipping at her. There’s a glimmer of respect there that builds and builds – but that’s not to say that there won’t be moments when they annoy each other! Sometimes, the more serious the job, the more you laugh. Life’s too short not to have a laugh. To me, that’s part of the joy of what we do. Well, being in Shetland during a summer heatwave wearing layers of cashmere will certainly stay with me forever that’s for sure! Beyond that, the beaches and the sea were incredible but one of the things that delighted meon adailybasiswere the sheep – who knew there are so many different types?