Anne, portrayed by Olivia Colman, pays a visit to her father, Anthony, played by Anthony Hopkins, in his apartment after he becomes increasingly agitated with his current caretaker. Anthony struggles with dementia, frequently forgetting significant life events and misplacing items within his own home, including his watch, which he insists is often stolen. During this visit, he surprises Anne with the news that he believes she is still married to James, leaving Anne perplexed as she reveals she has been divorced for five years and is planning to move to Paris with her new boyfriend.
The following day, Anthony encounters a perplexing situation when a stranger named Paul, portrayed by Mark Gatiss, seems to have taken up residence in his flat. Paul's assertion that they live together with Anne only adds to Anthony's confusion. Upon Anne's return from the market with dinner, she appears as another woman, Olivia Williams, which frustrates Anthony even more. In the midst of this chaos, Anne arranges for a new caretaker, Laura, played by Imogen Poots. When Anthony meets Laura, he claims a storied past as a dancer and insists he's self-sufficient, yet he is unable to shake the feeling that Laura resembles his daughter, Lucy, who he hasn’t spoken of for months, although he cannot recall why.
As the narrative unfolds, Anne takes Anthony to a doctor, who questions his memory. Denying any issues, Anthony goes on to boast about Lucy, who he believes is a talented painter. When Laura expresses her sympathy regarding Lucy's accident, Anthony is taken aback, claiming he has no knowledge of any such incident. Through a series of disorienting events, it slowly becomes evident that Anthony has been residing in Anne and Paul’s flat for an extended period, trapped in his own fading reality.
Tensions peak one evening when Anne returns home with dinner and she and Paul argue over a canceled vacation to Italy due to Anthony’s earlier erratic behavior. Paul expresses his frustration, questioning how long Anthony intends to impose on their lives, leading to an emotionally charged confrontation that leaves Anthony in tears.
In the subsequent scenes, Anthony's confusion deepens as he wakes up in a hospital corridor, haunted by visions of Lucy, whom he realizes tragically died in a car accident. He is left grappling with the loss in a nursing home, where a nurse, Olivia Williams, compassionately informs him of Anne's new life in Paris with Paul, while another caregiver, Mark Gatiss, checks on him too. This revelation pushes Anthony towards an emotional breakdown as he desperately longs for familiarity, lamenting his disconnection from reality, and he cries out for his mother, expressing his dread of "losing his leaves." The film beautifully concludes with imagery of leaves rustling in the trees, a poignant metaphor for Anthony's deteriorating grasp on the world around him.
