Warning: contains finale spoilers for Shetland series nine.Forget Professor Rossi and the world of spies, forget the mussel farming Harris men, forget Stefan Jakobson and Dr Mohan and their illicit experiments. Forget even the thankfully incorrect theory that young Noah Bett was the one who pulled the trigger on his mum Annie and her pal Anton Bergen. The real killer was somebody impossible to suspect.In its final episode, Shetland series nine chucked almost every previous diversion away to tell a new story: that of Noahs aunt and uncle, Noreen and Michael Stack. Ian Betts sister Noreen and her charity worker husband Michael had taken Noah in after Annies murder. No wonder the boy kept having nightmares, because was living under the same roof as his mothers killer.Who Killed Annie Bett and Anton Bergen?Annies sister-in-law Noreen Stack shot and killed Annie and Bergen at the Wethersta croft and then threw the gun into the sea, left Noah in the house with his mothers dead body, and drove home with her own baby Finn sleeping in the car. The murders werent premeditated, but accidental, opportunistic and driven by an instinct for self-preservation.Noreen was trying to save her family by covering up a rape committed by her husband Michael. Annie had been confided in by Lisa Friel, a client Michael had attacked at Shetlands HEM centre, and told Noreen that she planned to report Michael to the police the next morning. Instead of confronting Michael, Noreen chose to silence Annie. She followed her to the party at Bray, then on to the lab at Nesting where she picked up Anton, and finally to the croft where she confronted Annie, picking up the gun Annie had taken from Lisa (whom she feared would use it to get revenge on Michael) earlier that day.Noreen threatened Annie, who lunged for the gun, which went off, apparently accidentally, and killed her. Anton was drawn by the noise and Noreen shot him dead.Yes. Annie was planning to report Michaels crime against Lisa to Tosh. Because of Lisas criminal background and reputation for violence, and because there was no physical evidence of the rape, its assumed that Lisa would have had a hard time being believed if shed made the report herself. Community member Annie reporting her own brother in law though, would legitimise the report. Annie may also have wanted to report the gun shed taken from Lisa.Why Did Annie Call Rossi For Help?On the night she was killed, Annie called her former MI5 handler Euan Rossi in London using their secret code for needing help: Its getting late. That doesnt seem to have anything to do with Lisa Friel, or Michael and Noreen Stack, but to do with her and Anton Bergens plan to rescue Astrid from her fathers experiments and smuggle her off the isles and to Estonia to live with her mother.Read more In a major contrivance that turned out to have no impact on anything, Annie had identified Astrids stepmother Karin as a former Swedish intelligence agent codenamed Brutus, who had shot Annie in a bungled operation over a decade earlier. Perhaps she feared being recognised by Brutus and wanted Rossis help.What Was the Lizard?That was what little Noahs mind had transformed his aunt Noreen into in his nightmares about his mothers murder on account of the green, hooded waterproof coat she was wearing, which made her resemble a lizard to him. We know that Noah has an active imagination because he thought the two cranes at the Nesting lab site were a dinosaur. Noah had the breakthrough that the lizard chasing him and his mum in his nightmares was Noreen when they were standing outside the croft with her arms around him, wearing that same jacket.Where Did the Gun Come From?Lisa Friels ex-boyfriend Kyle Frost had used it in a drive-by shooting in Manchester months earlier, and then tasked her with getting rid of it. Lisa, however, kept the gun and Annie feared that she might use it to take revenge on her rapist Michael Stack. Annie took the gun from Lisa and brought it to the croft, where her sister-in-law Noreen used it to kill her and Anton.What Happened to Tosh in the Past?In series three, which aired in 2016, Tosh was abducted and raped to send a message to then-DI Jimmy Perez during an investigation into a double murder. That, and her natural empathy, made Tosh realise that Lisa Friel had suffered a similar attack and so she was able to learn the truth about Michael. Details of the rape were in Toshs police files, so though Tosh hadnt told Ruth about the attack directly, she knew that it had happened.What Happens Next?Series 10 was commissioned at the same time as series nine, so another six-episode mystery starring Ashley Jensen as DI Ruth Calder will arrive at some point in 2025.Character-wise, Ian Bett took son Noah away from the isles and to Edinburgh for a fresh start. His sister Noreen went to prison for the double murder of Annie and Anton, and his brother-in-law Michael was hopefully charged for the rape of Lisa Friel. Presumably John Harris was charged for the death of his son Fergus, and Stefan Jakobson and Dr Mohan were also charged for their unlicensed medical experiments. Professor Euan Rossi returned to London and sent Ian Bett a letter about Annies time as an MI5 analyst.Lisa and Angus left the manse and travelled on to more conspiracy theory investigation at the spaceport on Unst. Ruth and her brother Alan planned to spend time together, while the investigation took its toll on Toshs relationship with her friends, forcing her away from them and closer to her colleague Ruth.All episodes of Shetland series nine are available to stream on BBC iPlayer.