The Cuckoo episode 3 sees a breaking point for the family, with Alice still reeling from news she's adopted and Sian doing whatever it takes to get close to her.
Sian's scheming comes to a head when she visits her aunt to tell her the news, and makes plans to divide the family further. With Nick and Jessica already arguing about plenty, she takes it upon herself to twist the knife further.
In the penultimate episode, the main focus is on Sian's obsession with Alice, and just how far she'll go to ensure she can take her away from her adoptive family. Unfortunately, this has serious consequences for Nick and Jessica.
Here's what happened in The Cuckoo episode 3...
Sian gets to Alice
Following on from Sian confessing that she's Alice's mum, Alice is overwhelmed and says she feels sick, so everyone decides to give her some space. Nick and Jessica argue about how they told Alice, with Nick saying "it's always on Jessica's terms". Jessica brushes him off and tells him to stop being so cruel towards Sian, who helped Alice in the aftermath of the car accident.
Given the incident and the shock of finding out she's adopted, Jessica phones the school to inform them that she won't be in today. Sian goes to check on Alice and has an altercation with Nick, where she tells him to drop the act and reminds him that Alice could've been seriously injured. She heads into Alice's room and tells her that her parents don't care about her, and that they're "relieved" she's not biologically theirs.
Alice asks Sian why she gave her up, if she is her mum, and Sian tells her she was manipulated and taken advantage of, and it put her in an incredibly difficult position. Meanwhile, Jessica and Nick worry about the insurance, as they didn't admit Alice was driving the car when it crashed and they can't afford to be sued if they're found out.
Sian goes to visit her aunt again and reveals that she's told Alice the truth, saying that she plans to take her away, and her aunt protests saying that Alice already has a family and she's doing more harm than good. After an argument, the aunt asks her to leave, and Sian pockets a key on the way out.
Back at the house, Jessica and Alice finally sit down and talk. Jessica tries to assure Alice that she wanted nothing more than her, and always wanted to be her mother. Alice accuses her of being fake and says she knows she wishes she never had her, saying she's a liar. Nick lingers outside the room while they talk. Jessica goes on to tell Alice that her biological mother was "very troubled" and wouldn't have been able to take care of her, but Alice gets defensive.
Nick and Jessica enter a screaming match about recent events and Sian calls the police to report a domestic disturbance. She approaches Nick and asks to speak to him one-on-one, saying Alice asked her to come to him.
They go into the office and Sian tells him to look at this from Alice's point of view, but Nick gets defensive. She begins to blackmail him, and Nick asks her to leave, and Sian's behaviour turns quickly when she starts smashing her head against a picture frame, cutting herself with the glass. Nick is horrified and when Jessica comes in, Sian is acting as if he attacked her.
Police officers arrive having gotten a call about a disturbance, which Sian made earlier. Sian falsely claims Nick hit her and they arrest him as Jessica watches on, Nick is helpless at the police station, with everyone believing that he attacked Sian.
Jessica tries to reconcile with her daughter but Alice says the family is broken, saying that she overheard screaming and that's why the police were called and able to get here quickly. She claims Sian had called pre-emptively as they were both worried things might get violent, and says that Sian was bleeding so it was clearly serious. She tells Jessica to "stop pretending" they're a family.
Later on, Jessica catches Sian trying to access the safe. She gets angry with her for betraying her trust and throws her out, which prompts Sian to text Alice telling her to hold on and that she'll be back.
True to her word, Sian does come back and attacks Jessica by pushing her into the cupboard under the stairs, before locking the door. She grabs Alice and they drive away together, leaving Jessica trapped.