Line of Duty fans reckon they've cracked the case over the real relationship between Jo Davidson and Tommy Hunter - but it's a tough one to get your head round.
Eagle-eyed fans spotted a Post-it note that could hold a major clue.
It read: "Jo Davidson DNA has been identified at Farida Jatri's house. A match has been made to TOMMY HUNTER stating she is both his niece and daughter."
It's a total head-scratcher for fans of the hit BBC police drama, but could be a vital piece of information this series.
DI Kate Fleming (Vicky McClure) couldn't believe it when Team AC-12 revealed why they had her new BFF DCI Jo Davidson (Kelly Macdonald) under surveillance, and viewers were just as gobsmacked.
Jo's personnel file stated the deceased Samantha Davidson as her next of kin, and it was revealed that she's a partial DNA match for criminal kingpin and paedophile Tommy, who was killed off in series two.
DI Steve Arnott (Martin Compston) said: "That’s not the worst of it. There’s an unusually high percentage match," then mumbled the word "homozygosity".
Homozygosity is the state of possessing two identical forms of a particular gene, one inherited from each parent.
It seems to suggest some kind of incest in the family and that Tommy is both Jo's dad and her uncle, meaning he impregnated his sister, her mum, who is believed to be called Samantha.
One fan who spotted the clue tweeted a picture of the note and asked: "Did anyone else clock this post-it note? Niece AND daughter?"
Others thought that corrupt cop PC Ryan Pilkington (Gregory Piper) is somehow involved too.
One tweeted: "Maybe Jo is the missing Teenager that was with Tommy. Ryan is their son it’s his DNA in the flat. He’s been manipulating Jo. He’s the mastermind. Ted has her undercover to stop him."
Another posted: "Jo is Tommy Hunters niece and daughter with the homozygosity in their DNA but did the incest continue and Ryan is Jo’s son, the lingering looks between them, the over the top way he calls her Ma’am (mum) and someone had to have fast tracked him into MIT"
While one questioned: "So if Tommy H is Jo’s dad AND uncle, who is her mum?!?! Guessing Jo doesn’t rate her much as she is lobbying glasses of wine at her photo?!"
And another quipped: "I don't think I need as much therapy as Tommy Hunter and Jo do."
* Line Of Duty airs Sundays at 9pm on BBC One
