However, when Peter Ayre’s car is spotted in the hospital car park the night Ellen’s body went missing, the police head to his house, only to find a horrific scene unfolding. Peter is in the middle of a strange ritual, where he is burning a fire in the grass in the shape of the mysterious symbol from Ellen’s tattoo and chanting and singing around a bonfire, which at closer look has Ellen’s body lying in the middle of it. But if that wasn’t enough, there’s one more twist in the episode when Calder finds out her father had an affair with Ellen’s mother, Stella Quinn. Does this mean Calder has been investigating her own sister’s murder without even realising? What happens in episode 4? 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. Tosh is very comfortable in the role so she has definitely been doing it for some time and has really found her rhythm. She has an easy rapport with Sandy [Steven Robertson] and Billy [Lewis Howden] and the team seems to be functioning well and not dealing with anything too grizzly. She also has a great connection with Harry [Tibu Fortes], the new procurator fiscal, who really champions her. 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.

She is a wonderful mix of an absolute hoot and a consummate professional. There were days when I laughed so hard my stomach hurt and I was in danger of crying all my make-up off. But we never, ever lost focus or took our eyes off the ball. Figuring out our chemistry together was an outright pleasure and I'm really proud of what we created together. There will be a different dynamic with Ruth amongst the regular characters and a few more newinteresting characters to enjoy. However, the integrity of the show and the world that has been created will remain very much in the same tone as the last seven seasons. It's a real privilege to be asked to lead this show into a new chapter. I can’t wait to be working in Scotland again. I have missed it!”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? Over the last 10 years, we’ve seen Tosh change from the chocolate vodka hungover new recruit to the temporary DI in charge…what’s that been like for you? And then there’s the weather! One minute we had this horizontal rain and the next, a heatwave and it was like the tropics and everyone was going wild swimming. I felt like I was on my holidays.

How do Ruth and Tosh get on when they first meet and how do you see their relationship progressing? There’s absolutely scope for them to get on and work together, they just need to get into each other’s groove. There will, of course, be moments of conflict which is always great because if everybody gets on all the time, it’s a wee bit boring. This cast was extraordinary. Because the show has been reconfigured, it felt like a new beginning in a way and everybody really embraced that. It felt like we were all creating this new thing together, taking ownership and really giving it everything. The chemistry among everyone was off the scale. We had so much fun together, and we worked hard and we really worked as a team. 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.Tosh would describe Calder as an extremely skilled and experienced police officer who doesn't suffer fools and doesn't mince her words, but who has an emotional hinterland and a softer side that she catches glimpses of and is very curious about. This new series of Shetland has a stellar guest cast – what was it like working with the likes of Phyllis Logan, Dawn Steele and Lorraine McIntosh? I would say that Phyllis, Dawn and Lorraine really brought everyone together. They are wonderful, charismatic, generous women who really led the way with their performances and their professionalism. Sometimes it was hard to concentrate during the scenes because watching them perform was so distracting, like being in the front row of a hit show. Inspired by Ann Cleeves' Shetland novels, Shetland is a Silverprint Pictures production for the BBC.

Like any close relationship with someone you have to work alongside intensely, there are moments when it flows and moments when it doesn't but they are both fiercely committed to their work, they always have that in common, and it is this dogged pursuit of truth and justice that is the engine that drives them as a team. On top of the twists and turns of the case, Calder is faced with figures from her past including her ex-boyfriend Cal Innes (Jamie Sives) and estranged younger brother Alan (Steven Miller) – now the minister of their late father’s old kirk. However, these siblings have starkly different views of their shared childhood. The entire cast was amazing but I have a special place in my heart for the inimitable Don Gilét [who plays hitman Howell]. The first couple of weeks were quite disorientating for me as I found my feet in this new world ofShetland. The first day I remember really loosening up I was chasing him [Don] down a beach. I was in pain with laughing. He's such a one-off, insanely funny and makes every day you're working with him memorable and special.

Gaynor Holmes, Commissioning Editorfor the BBC adds: "I am absolutely delighted that Ashley is joining the stellar cast of Shetland. Ashley is an immensely accomplished and well-loved actress who is known internationally and we can’t wait to welcome her into the Shetlandfamily when filming begins in the spring." The world of Shetland police HQ is as we knew it - warm, reassuring and familiar. But change is coming and with it, fresh challenges for the team. 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. Phyllis Logan, who plays Grace, is among the fantastic guest cast (Image credit: BBC) What’s the plot?

We have both grown older, we are both mothers, we both have a huge amount of experience under our belts. It's nice to be able to chart that journey for myself both on and off camera but this series, to be standing in front of the board, taking charge of the team...I felt like I had grown wings. As you view disk to disk you get to know and understand the characters and their feelings come through. It’s clear from the off, Calder has no love for Tosh’s adopted home and their journey into the dark recesses of Shetland's past and present will test their partnership to the limit. 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?

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The camera work is good. Personally I do not like to many close up shots of the actors. In real life I find I like to be a few feet away, which I find is more realistic. So it’s not Tosh that Calder has an issue with – it’s the two different approaches to work. Both are valid and, as they start to work together as a team, they see their strength together.