Shetland star Alison O'Donnell: 'Secrets are going to come out'

Speaking to press, O'Donnell explained that her character is "immediately" concerned by Annie's absence, but doesn't consider it to be a police matter until pushed by Calder to look deeper.

She said: "Her friend has requested they meet, she had something important she wanted to talk to Tosh about – on a professional level – but when Tosh arrives at the agreed place and time, her friend is not there."

Things "escalate" when Tosh reaches out to everyone in her immediate social circle, including partner Donnie (Angus Miller), and nobody has a clue where Annie could be.

The nightmarish realisation causes Tosh to throw herself into a formal investigation – no matter the cost to her own privacy or relationships.

O'Donnell explained: "Tosh has an unshakeable integrity. She's always going to do the right thing by the investigation, which may not always sit well with her friends.

"Everyone is feeling compromised, stressed and mistrustful, and these friendships are going to be tested."

She continued: "In an investigation like this, every stone must be unturned and a lot of secrets are going to come out. But for Tosh, this collateral damage is unavoidable.

"She feels the discomfort of it, but her primary goal always is to unearth the truth and get justice, however that may look."

O'Donnell went on to reveal that Donnie, who was first introduced back in season 5, also feels "very close" to this case, which could very well drive a wedge between himself and Tosh.

"His best friend becomes a key person in the investigation, and while he supports Tosh, he is pulled between his loyalty for his friend and his proximity to how the police investigation develops," she added.

"They live in a small community where conflicts-of-interest are inevitable, but people are human and fallible and flawed and relationships have weaknesses. This is a bumpy road for them."

Shetland returns to BBC One and iPlayer on Wednesday 6th November.

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