EXCLUSIVE: Shetland's Steven Robertson on Sandy's shocking discovery in episode 5

"Oh, it was just extraordinary — once we knew the whole idea and the changes that were going to come, and I got told we were going to have such an incredible actress coming in, it was just 'oh wow, that is really intelligent, brilliant casting'. That whole dynamic of Tosh and Ruth meshes together so beautifully, and having that strong dual-female front to the show, everything just felt instantly right about it to me when it was being described.

"We obviously know Paul's [Logue, Shetland's lead writer] writing really well, because he's written for the show for many series now, so I knew that absolutely the right person was becoming the lead writer. I love his work because it is so full of detail: nothing is by-the-by whether it's a line of dialogue or a very specific point about a location, it's always linked to a backstory or a specific character."

"Where do you start?! First and foremost, because I don't think people talk about these things enough, she is such a lovely human being. She is so professional and a brilliant actress — I've loved her work for years, shows I grew up with here in Scotland like Roughnecks and Takin' Over The Asylum and all the amazing stuff she's done since. She probably had the hardest job of anybody this series, because she's got to launch a new character, but because of all of her experience and ability, she thought about that and worked on that in advance to the extent that she knew where she wanted to go with the character.

"Calder herself has a lot of depth — as the show twists and moves and takes you one way or another, you get to see Calder from different sides, you get to see the pressures that took her away. There's so much complexity to the character, suddenly having to be back on the islands that she wanted to leave, and you juxtapose that with Tosh who isn't from the Shetland islands but is so proud of Shetland and has been so involved with so many families and now she's working with Calder who isn't really sure she wants to be there — it's like firecrackers everywhere! I can't say enough about how splendid the whole experience was."

"For me, that was a gift. There's something about Sandy's simplicity — and I mean that in a really positive sense — that I absolutely love, and it's something I've always tried to cultivate and take really good care of. He's made mistakes in the past, and he gets stressed by things — as he should, we're making drama! — but he always comes back to the central points that he has a strong sense of right and wrong, and he's incredibly loyal.

"What I think is fascinating in this situation is that Sandy would never question Calder's authority because of everything she's achieved off-island — she's from Shetland and she's had this amazing career working in London, so he has nothing but respect for all of that. At the same time, Tosh would be his absolute go-to, his boss, but when the drama kicks in, there's a slight 'servant to two masters' thing going on with Sandy! He's like 'I really want to work with Tosh, but I know this person is onto something, and I know she's from here and maybe has an angle she can't reveal to me'. Sandy always wants to do his job to the best of his ability, but does he do that by going to the left, or to the right? It's a joy to play that with two fantastic actresses!"

"Absolutely! Again, one of the things that's amazing about Paul's writing is that he allows the space for that, and the fact that Ashley was so open to having these conversations was just brilliant. It's a small place, we're talking a population of 23,000 at the most, and even when people move away, that information can't go anywhere. So there's no way we could approach that conversation and not be like, 'we would have known who each other was'. Calder's father was very prominent, he was the minister for one of the districts, so it kept that internal life going, and it was so much fun to play that with Ashley."

"The really great thing I love about that storyline is that it actually starts with no connection to the main story. Sandy's bread and butter is staying on top of things like the drugs that are being illegally brought in, that's the nuts and bolts of good, solid detective work in Shetland that he is all about. In terms of the backstory of this series, that's already a big drive for Sandy before DI Calder turns up and they all get taken off on this much more serious investigation.

"So when it turns out that his day job is fundamental to moving the case forward, that's really big for Sandy — he can't not act on new evidence to something that is of such importance, and that's going to have a ramification on the case and his relationship with Calder as he takes that forward."

"Sandy Grierson, who plays Peter, is an incredible actor. It was a very late night on a very cold hillside, and he had to play such an extraordinary part where he just had to shut out the cold while our block one director Andy [Newbery] got all the right shots, so we all just tried to support each other and remember how lucky you are to be making — dare I say it — quality television! Those are my lasting memories of that night, just how incredible Sandy is. You can see all the work he had done to be able to do that, vocally and physically, and it was a joy to watch."

"I'm lucky enough that the whole thing exists and is made in my homeland that I love so much, but what's extraordinary is that there are so many crew and cast that have come back and are integral parts of the show, there are now people coming up here to work on this, suggesting to me places I should go: 'have you ever been to such-and-such beach?' And I'm like, 'do you know, I haven't!' 'Well, you must!'. 

"That's one of the biggest gifts of this show: the location work is hard here because the weather here in Shetland can be absolutely incredible, but it can also be quite changeable and quite challenging. In what could be described as a difficult shoot, people want to come back, again and again, to work on the show, because they have a great love for the show and the islands."

"I just hope that people love it as much as we love making it. It would be amazing if people continue to love it and we get to take it forward again, and continue to work with the most incredible people. I'm very biased, being able to share my beautiful homeland with a really wide audience, and the way that it's received around the world, is deeply moving to me!"