The episode 6 of "The Chestnut Man: Hide and Seek" Season 2 unfolds with Bjarke revealing to Mark that it was actually little Thea who killed and crucified the cuckoo chick. Thor enquires with Signe about Marie's whereabouts, but Signe asserts that she is depressed and should be given space. Thor's concerns persist, and he discovers a suicide note. He finds it peculiar since Marie would never refer to the children as "kiddos." The siblings panic, and Michael calls the police.
Marie is tied up in an isolated cottage. Signe views the Holsts as family and is angered by Marie's actions that disrupted their life. Like a mother, Signe claims that Emma ruined her family. After Staal killed himself and her mother abandoned her, Signe went through various foster homes until she found happiness with Roy and their children. However, that happiness was shattered when he and Emma started an affair. This is why Signe killed Emma. To maintain her cover, Signe decides to kill Marie and frame it as a suicide. Marie tries to connect with her over their shared grief, but it was actually Signe who lured her with the support group flyer. Seeing Marie's sadness helped Signe feel better. Though she started seeing Marie as a friend, Signe asserts that she doesn't need her, as she will take in Thor and Molly instead.
Esra reopens the case but keeps Mark out of it. Sandra traces Thea until she finds her as Signe Bohm-Moller, married to Roy and working as a therapist at...the agency. The police learn that Roy and their children were killed in a car accident caused by Roy's distraction during an argument with Signe for a divorce. The agency's CCTV footage shows Signe being upset on little Aska's behalf that Zara cheated and divorced her dad. And Signe's home is still full of toys and schedules for her children. Sandra deduces that Signe became obsessed with avenging children affected by their parents' infidelity and divorce.
Mark goes to a youth facility that was Thea's last known location. Agnete, the manager, shares that Thea was unstable and would go to her father's cottage to clear her head. Sandra refuses to give him the cottage's address and reminds him that he is still grieving. This gets to Mark, and he regrets not being there for Le. He tries to check in but, having had enough of his hot and cold behavior, Le tells him to leave her alone. She is caught for underage driving and lashes out at Aksel, who is not the father figure she wants but rather Mark. She misses Naia, and Aksel comforts her. They plan their future, and Le regrets how she ended things with Mark.
The police receive Michael's report and realize that Signe has kidnapped Marie. Sandra tries to update Mark but cannot reach him. She finds his car near the location where Signe answered Thor's call. It turns out that Agnete gave Mark the cottage's address. Seeing Mark approaching the cottage, Signe panics and throws Marie into an empty swimming pool. Alone, Marie quickly unties herself. Initially, Signe plays the naive, nosy countrywoman but is seen through by Mark. She stabs his leg, and he runs off. A cat-and-mouse chase ensues, with Mark hiding in the water and almost freezing. He emerges from his hiding place, and Signe drowns him. As he passes out, he sees Naia. Just then, Marie brutally stabs Signe multiple times, killing her and saving Mark.
It cuts to two weeks later. Though Marie may be charged with murder for stabbing Signe multiple times, she will be there for Thor's graduation. He decides to wear Emma's graduation cap so she will be with them. The family bickers, but Marie is glad to have them by her side. Mark visits Naia's grave and meets Le. He buys a house with an extra room for Le and quits Europol to find a job in the country. Le is pleased, and they hug each other.
