Introduction to series four from Shetland’s long-term collaborator David Kane, writer on four of the six episodes.

Every writer has half-formed ideas flying around in their head, circling, like birds looking for somewhere to land. Elmore Leonard described putting ideas aside for the future as "hanging them up for parts". I like this - it makes me think of the writer as a mechanic putting an old engine together, rather than writing a script, and finding themselves looking around for that spare part they need to finish the job. And there it is, hanging up on the wall gathering dust.

That’s how the new series of Shetland started. I had been interested in writing about miscarriages of justice for many years and an idea I’d been messing about with was ‘hung up for parts’. When I was asked to storyline the series it was time to take it down from the wall and see if it would fit into the engine that is Shetland.

The story of a man being released from prison for a crime he apparently didn’t commit, returning to his small community, opening up old wounds and resentments, seemed a natural fit for series four. How would Jimmy Perez deal with a situation where everyone on the islands thought someone was guilty, but he wasn’t sure? And when a similar crime is committed to the one this man was convicted for, how much benefit of the doubt can Perez give him?

I always feel that when you write a detective story, it should be more than just a murder mystery - it should be about something. This story looks at how society treats people who have been wrongly imprisoned and goes to the heart of what we mean when we talk about community.

The reopening of the original case draws everyone into this tangle of thorns, including Duncan and Cassie, and Perez finds himself with his loyalties divided in a way they’ve never been before.

Having that as the spine of the series, I knew we needed to take Perez out his comfort zone and bring in other suspects for the horrific murders that unfold. With that in mind Perez also finds himself following a suspect to Bergen in Norway and becoming drawn into the dark world of Far Right nationalist groups. Again, a subject I have always been horrified but intrigued by. So when Douglas himself suggested it would be good to have a Norwegian connection, this storyline, inspired by research I was doing on these groups, crept into the story.

But ultimately the series has to be about Perez’s relationship with Shetland and its people. He finds himself under a great deal of emotional strain as his sympathy for the victim’s grieving family battle with his empathy for the tortured man whose life was stolen from him. How do you stay objective and keep your focus when all around you others lose theirs?

There is a definite theme running through the series about parent-child relationships, and that is something Perez is always keenly aware of, honing in on those emotions - and clues.

Now that we have a longer format for Shetland we can’t use the books as source material, as we’d need to change so much it would not do them justice (and probably upset the fans of the novels) so it is better to create new stories while maintaining the essence of Ann’s books and characters.

The crimes in her books feel emotional and rooted in Shetland culture, and that is what we aim for in this new series.

Watch the three previous trailers below: