In London, Anne (Olivia Colman) enters an apartment looking for her father, Anthony (Anthony Hopkins). She finds him and is upset with him because he has caused another caretaker/nurse to quit (the third one) after he got threatening and aggressive with her and accused her of stealing. He claims that she was stealing from him and stole his watch. Anne asks him if he’s looked under the bath, in his hiding space where he puts his valuables. Anthony is angry that she knows about this, but goes to look and finds his watch there. Anne asks if he’s taken his pills, and calls her a worrier, and says his other daughter (Anne’s sister) wouldn’t keep badgering him that way. He asks where she is, and Anne doesn’t answer.
Anne tells Anthony that she’s going to be moving to Paris – she says they already talked about it but he doesn’t remember. She says she’s met and fallen in love with a man named James and is moving to London to be with him. Anthony feels abandoned, but Anne says she will still be able to come to see him on weekends, she just won’t be able to check on him every day. She notes that if he refuses to have a caretaker, she’s going to have to find some sort of other arrangements. Anne leaves and Anthony finds groceries that he begins putting away, but then he hears a noise in the apartment and begins searching for the source of it.
Anthony enters the living room and finds a man (Mark Gatiss) reading the paper. Anthony is startled and demands to know what he’s doing in his apartment. The man says his name is Paul and that he’s Anne’s husband (of ten years), and that it’s his apartment, not Anthony’s. Anthony says he thought they were separated. The man, clearly troubled, calls Anne and says her father wants to see her. Anthony tells the man he thought Anne was moving to Paris – he insists that’s not the case. He tells the man he has no need for a caretaker and that he will absolutely not leave his apartment – the man tells Anthony it’s not his apartment, and that he moved in with him and Anne after his last caretaker quit. Anthony doesn’t believe him.
Anne arrives home – only it’s not Anne, it’s a completely different woman (Olivia Williams). Anthony demands to know who she is and where Anne is – the woman who claims to be Anne is horrified, telling Anthony it’s her and that she just went out to get groceries to make them dinner. The woman is saddened that Anthony doesn’t recognize her. He says he was just talking with her husband, but she says she’s been divorced for five years. Anthony insists the man was there, but can’t find him in the apartment, and becomes panicked and dejected. The woman comes to check on him, worried and suggests he take his medication, which she gets for him and helps him take. He asks the woman if this is his apartment, but she doesn’t answer.
Anne returns to the apartment, on the phone telling someone about how some days Anthony doesn’t even recognize her. Then Laura (Imogen Poots), the new caretaker she’s brought to try out with Anthony arrives. Anne warns Laura that her father’s behavior can be unpredictable, and that’s why she moved him into her place but she can’t manage everything and needs help. Anne introduces Laura to Anthony, who is delightful and charming, much to Anne’s surprise. He realizes he isn’t wearing his watch and goes to retrieve it. When he returns, he tells Laura that he has two daughters, Anne and Lucy and that Lucy was his favorite, hurting Anne. He says Lucy is a painter and wonders why he never hears from her. Laura asks what he did for a living – he was an engineer, but tells Laura he was a dancer and shows off some moves to delight her. Laura laughs, and Anthony tells Anne Laura reminds him of Lucy, which Anne agrees.
Suddenly, he then viciously insults Laura out of nowhere, startling her. He then goes on a long tirade about how Anne has always wanted his apartment, and has now moved in with him and is clearly trying to trick him into thinking he can’t live on his own so she can shuffle him off to an assisted living facility and steal the apartment from him. He vows to outlive her and tell everyone at her funeral she was heartless. He leaves, and Anne is devastated, apologizing profusely to Laura, who says this behavior isn’t uncommon. Later, Anne accidentally breaks a cup in the kitchen, and cries as she picks up the pieces. She imagines smothering her father with a pillow.
Anne’s husband Paul (Rufus Sewell) comes home and asks how it went. Anne tells him about Anthony’s encounter with Laura and gets a little tense with him. He asks what that’s about, and Anne says when she came home with the chicken he didn’t even recognize her. Anthony joins them since dinner is almost ready, but he doesn’t recognize Paul. He sees Paul’s watch and becomes suspicious. He tells Anne about it and she goes to find his watch in his hiding space, while he talks with Paul, asking him about the origin of his watch. He talks a lot about Lucy, and Paul stops him and bluntly asks him long he’s going to keep hanging around.
Anne takes Anthony to a doctor’s appointment, where Anthony tells the doctor about Anne’s plans to move to Paris. She’s shocked as she says she has never been going to Paris and will be staying in London. Later, at the apartment, Anne helps Anthony get dress and he kindly thanks her. He then overhears Anne and Paul talking – Paul is telling Anne they need to put Anthony in a facility, and Anne says they’re just about to have a new caretaker starting. Paul says there will come a moment when there’s nothing else they can do, and then they notice Anthony listening. When they’re alone, Paul tells Anthony he sometimes wonders if he’s acting forgetful on purpose. He tells Anthony how they had to cancel a trip to Italy after Anthony’s last caretaker quit. There is definite tension between Anne and Paul – Paul is clearly tired of dealing with Anthony. When they’re alone, Paul says they need to put Anthony in a nursing home, and they have the same conversation Anthony overheard before, and he walks in on them again.
The next morning Anthony is in his pajamas, and one second Anne is there, then suddenly it’s Laura. She brings him his medication, and he cruelly asks her if she’s “retarded” and tells her to stop talking down to him. When Anthony tells Laura she reminds him of Lucy, Laura says she heard about what happened to her, the accident, and apologizes, but Anthony has no idea what she’s talking about and Laura changes the subject. The man enters again, clearly alarming Anthony who doesn’t know who he is. While Laura leaves to get Anthony’s clothes, the man bluntly asks him long he’s going to keep hanging around, the same as Paul did. He asks how long he’s going to keep ruining his daughter’s life, and begins cruelly giving him little slaps to the face. Anthony begins crying, and Anne hears and runs in and sees Pauls standing next to Anthony. She tries to console Anthony, who is crying, and says she found his watch and that she made him dinner. Anthony says he thought is was morning, he’s in his pajamas.
In the middle of the night, Anthony hears voices. He gets out of bed to follow them and is suddenly in a hospital hallway. He searches for Lucy, and walks to a hospital room, where he sees Lucy severely injured and asking for him. The next day, Anne tells Anthony Laura is starting today. The doorbell rings, and Laura arrives – except it’s not Laura, it’s the woman. Anthony tells Anne this isn’t her, but Anne insists it is. Later, Anne goes to talk to Anthony, but this time his bedroom is one inside a nursing home. The woman is there – but she’s a nurse named Catherine. Anne asks him if they could come to a decision that moving here would be best for him – she says she’s moving to Paris. He wants to know where Lucy is, and Anne begins to cry – Anthony comforts her and holds her cheek.
Anthony wakes up in his room at the nursing home, and Catherine comes in to help him. He doesn’t recognize her, but she says she’s been helping him for a few weeks. He keeps asking for Anne, but Catherine shows him Anne’s postcard from Paris. The man enters – he too works in the facility and his name is Bill. Anthony asks who that is, then asks who he himself is, and asks if his mother is coming to see him. Anthony then begins sobbing uncontrollably, asking for his mother, and saying he has no idea what’s going on anymore – he feels like he’s losing all the leaves from his branches. Catherine comforts him, saying they’ll get dressed and then go for a walk in the park. She assures him things will be okay. Outside, the tree branches blow in the wind.