When DI Ruth Calder (Ashley Jensen) returned to her native Shetland in season 8 to retrieve Ellen Quinn, a runaway witness in a gangland shooting, she did so reluctantly.
Shortly after she turned 18, Ruth packed up her belongings and left the isles for good – and she had no intention of returning.
But 30 years on from her exit, she's back, much to the delight of ex-boyfriend Cal (Jamie Sives) and the local gossipmongers.
In the short time we've spent with Ruth, who arrived following Jimmy Perez's departure, we've not learned an awful lot about her, but we do know she had a strained relationship with her father, who was a reverend, a job her brother Alan took on following his death.
But details about the specifics of their feud were firmly under wraps.
In tonight's episode (Wednesday 15th November), however, we discovered that he had an affair with a woman called Jean Ferguson (Jennifer Black) while Ruth's mother was dying in hospital.
"It was a difficult time," said Jean, who wanted to "clear the air" with Ruth.
"I'm sure it suited you to think of me as the evil woman these past 30 years, but I'm not. I loved your father, and I think he loved me. I'm not ashamed of it."
But Ruth had no desire to listen.
"Well, it didn't seem all that difficult when I found you in my mum's bed," she responded.
It's a deeply uncomfortable moment, with both parties clearly still hurt by the events of the past. But if Ruth's opinion of her father was low before, the piece of information that Jean next delivered completely floored her.
"I'm not a police officer, but isn't there stuff about conflicts of interest?" she asked the detective.
Ruth, confused by the direction the conversation had taken, demanded that she elaborate.
"I wasn't the only one, you know," said Jean. "After me, there was someone else."
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In a shocking turn, that individual is revealed to be Ellen's mum Stella, who was "half his age".
"Even I was ashamed of that," added Jean.
Ruth was lost for words, particularly given an earlier conversation she had with Stella in which she told the DI that she used to attend youth groups at the church on a regular basis.
"He talked about you sometimes, your dad," she said. "I got to know him quite well."
Where does Ruth go from here?
Shetland season 8 continues on Wednesday 22nd November at 9pm on BBC One and 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.
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