The Cuckoo ending brings this story to a close, with a huge twist along the way as we finally unravel what's going on with Sian.
We pick up the story after Sian ran off with Alice, after attacking Jessica and locking her in the cupboard. The two of them drive off while Jessica is trapped, and Nick is still at the police station, so Alice found herself in a difficult position.
The episode builds to a thrilling climax where we learn the truth about Sian, as Jessica and Nick scramble to get their adopted daughter back from their lodger. Here's how it went down...
The Cuckoo ending explained: Was Alice Sian's daughter?
The episode opens with Jessica attempting to break down the door, after Sian left her trapped in the cupboard under the stairs. Meanwhile, Nick is released from the police station on bail and is told not to go anywhere near Sian.
In the car, Alice asks Sian if they should go back because she's worried about her mum. Sian replies saying "Who?" and she corrects herself, calling her Jessica instead. She tells her not to worry about people who don't care about her. Sian has to pull over so Alice can be sick. When she's feeling better, Sian says she's taking her somewhere "really special".
Jessica eventually manages to break down the door with brute force, where she frantically searches for Alice before calling her phone, but it goes straight to voicemail. Nick comes home and Jessica tells him that Sian has taken their daughter.
Sian and Alice stop at a petrol station and Alice tells her she needs the bathroom. There's one round the back so she goes, despite Sian's protests that they're on a schedule and need to keep moving.
Back at the house, Jessica and Nick remember that they installed a tracker app on Nick's phone to keep track of Alice in case of emergencies, and they use it to see where she's gone. Meanwhile, Alice uses her phone away from Sian, who watches her in the wing mirror.
Nick and Jessica follow the directions to Alice's current location, while Sian catches Alice in the middle of sending a text, causing her to quickly put the phone away again with the message left unsent. Sian tries to calm Alice down, telling her that Jessica and Nick don't want her, and goes on to say that Jessica confided in her and told her some information she'd kept secret.
Alice gets upset when Sian tells her that Jessica called her a sticking plaster, something that you'd get a woman who has everything, and that Nick is the kind of man who thinks they can just take whatever they want, before discarding it when they're bored. She starts crying, believing Sian's words to be true.
While this conversation is going on, Nick and Jessica close in on the petrol station, where the waypoint had directed them. However, when they arrive, they find her phone abandoned and her half written text. They decide to go to the police, but given Nick's earlier incident, they're reluctant to believe him.
An officer says it's likely that Alice tried to remove herself from the situation, which they still believe to have been an attack on Sian by Nick. They do their best to argue their point, and the police search Alice's room for potential clues, before concluding that they'll open a missing persons' case and distribute a photo of her, but Nick and Jessica are frustrated, claiming she's in danger.
Sian and Alice arrive at a caravan park, which Sian says is home. Alice is confused and says that they can't stay there, telling Sian she wants to go back to Jessica and Nick, but she stresses that they don't want her back. Alice gives in and the go inside one of the static caravans, where Sian reveals Alice was born. She locks the door and pockets the key.
Jessica and Nick visit Sian's Auntie Fay, who was her reference for the lodging. She asks them to leave and says she can't help them, but Nick forces his way into the house and begins calling out for Alice. Fay leads them into the kitchen, saying Sian has done many things in her life, and has only ended up hurting herself.
Sian sits Alice down and explains what happened. She said that she fell pregnant after getting involved with a boy when she was younger, and that her mother had been disappointed by her actions. Sian assures Alice she'd never be disappointed in her, before going on to reveal she always wanted her. She tells her that her mother wouldn't look at her, and that Aunty Fay had intervened, so she ran away to the caravan park where she gave birth by herself.
Back at Fay's house, she shows Nick and Jessica a photograph of a younger Sian when she was pregnant, posing outside a static caravan. Fay reveals that the baby had died during childbirth, and that Sian had hired people to find adopted babies with the same birthday, so she could replace the child she had lost. Nick asks where the photograph was taken, and they leave, heading to the caravan park.
Meanwhile, Sian becomes more erratic, telling Alice she knew she wasn't dead and that she'd never "let go of her baby" like her own mother had. Alice realises that Sian had been in denial about the fact her daughter had died, when she says she'd tried to connect with her but she'd been "sleepy". While she's talking and looking out to sea, Alice sneaks off and begins to flee the caravan park, and Sian begins looking for her.
Sian eventually catches her and Alice tries to convince her she was just pretending, but Sian hits back asking if she thought it was a joke when she was taken away from her. She drags Alice back to the caravan and gets angry with her, saying how awful it felt thinking she'd lost her again. Alice tries to convince her that she's not her baby, and that she wouldn't say anyone if Sian just let her go, but Sian ignores her and tries to redirect the conversation.
Alice attacks Sian and asks her for the keys, while Nick and Jessica arrive on the scene. Nick runs into Sian who has armed herself with a knife, and ends up stabbing him. Jessica catches up and makes a tearful plea to Sian, saying Alice is not her daughter and she wishes she could bring her back but she can't. Sian attacks her, pushing her to the ground and saying Jessica can't take her daughter away.
Thinking quickly, Alice addresses Sian as "mum" and tells her that she remembers, which coaxes her away from Jessica so she can get back to her feet. Sian has a breakdown and says she held her too close and she stopped crying, and Alice says she forgives her.
Sian begins to back away towards the cliff edge, where she falls back and says she just wanted to be with her baby. Jessica and Alice hold each other and cry, before the scene cuts.
In an epilogue, Nick survived the stabbing and the family is packing up their belongings into a removal van. The police arrive to confirm the body has not been recovered, but they notified a next of kin about what happened. Jessica and Alice appear to be closer.
A final scene shows another young woman answering a knock at the door, where a woman who appears to be Sian is standing, strongly suggesting that she is lodging in another house ready to repeat the same thing all over again.
