Shetland's Calder is in uncharted territory – and Tosh comes under fire

She had recently arrested Annie's estranged husband Ian, news which was greeted with confusion and anger by several locals, and by Tosh's partner Donnie, who is a close friend of his.

Eventually, Ian was released after Joni, one of Annie's friends, informed Tosh that she and Ian had been having an affair, and that he was with her the night Annie was killed. The lab results also proved that the blood on Ian's shirt was his own, not Annie's.

But John Harris, a mussel farmer who Annie had been living with prior to her death, still believed Ian had played a role in his wife's demise and purposefully mowed him down with his car.

"Obviously he believes Ian was the one who killed Annie," said Tara. "Wonder where he got that idea from..."

That morning, Donnie had also been needling the detective about her treatment of his friend, which had been an ongoing debate in their household of late.

Speaking previously to RadioTimes.com about how the case impacts Tosh's personal dynamics, Alison O'Donnell said: "I think it's the first time that we've seen the personal and the professional clash to such an extent for her.

"It's an island, it's a small, close knit community, there are always little conflicts of interest, and it's often people that we already know that we end up interviewing in the course of the proceedings. But this one for her is really close, too close for comfort."

Talking specifically about how it affects her partnership with Donnie, O'Donnell added: "Their relationship is kind of thrown into a bit of jeopardy because his close friends are involved, so it's a really difficult path to tread.

"Like most relationships, they do have challenging moments, but this felt like a different sort of thing. This is a bit more profound and fundamental to what their relationship is and how they both see each other, and how they see the relationship and their life in this small community, and what the priorities are.

"And I don't think that Tosh is going to come out of this unscathed. At the conclusion of the series, her relationships are not what they were when the series begins."

Read more:

• Shetland star says show has "double identity" post-Jimmy Perez
• Shetland's Alison O'Donnell would "hate to overstay welcome" on show

And it wasn't just Tosh who was feeling the weight of it all at the season halfway point.

Calder found herself becoming attached to Annie's young son Noah, who was rendered mute in the immediate aftermath of his mum's murder and continues to suffer from panic attacks.

Despite initially being met with silence, the detective was the first one who coaxed him into talking about his mum, if only briefly, using maths and dinosaurs as a way to break through.

And their latest interaction has clearly left a mark on her because she rang Annie's sister later that evening to check in on Noah.

"What am I doing?" a visibly emotional Calder whispered to herself after she put the phone down.

Annie's friend and former maths professor Euan Rossi also picked up on her fondness for Noah when he paid her a visit at her home.

"You act like you care about him," he said.

But Calder was keen to brush off that observation.

"He's just a witness," she responded.

"Best not to get too attached," added Euan, to which Calder said that in order to do her job properly, she had to retain an emotional distance.

But evidently, that is easier said than done.

Shetland seasons 1-9 are available to stream on BBC iPlayer. Ann Cleeves's Shetland novels are available to buy now.

Check out more of our Drama coverage or visit our TV Guide and Streaming Guide to find out what's on. For more from the biggest stars in TV, listen to The Radio Times Podcast.