The film opens with poignant on-screen captions revealing that a medical breakthrough in 1952 has allowed human beings to live beyond 100 years. Kathy H (portrayed by Carey Mulligan), now 28, serves as the narrator, reflecting on her childhood at a boarding school named Hailsham and her life following her departure from its gates. The first act immerses us in the world of young Kathy, alongside her companions Tommy (Andrew Garfield) and Ruth (Keira Knightley), as they navigate their formative years during the late 1970s.
At Hailsham, the students are strongly encouraged to create art, with the finest pieces displayed in a mysterious collection known as The Gallery, overseen by a woman called Madame (Nathalie Richard). This world is shattered when a new teacher, Miss Lucy (Sally Hawkins), quietly reveals their grim fate to the students. She shares the harrowing truth that they are destined to become organ donors, facing an early demise—this revelation leads to her dismissal by headmistress Miss Emily (Charlotte Rampling). As the years unfold, Kathy develops feelings for Tommy, but Ruth intervenes and begins a relationship with him, complicating their childhood bonds.
In the second act, we find Kathy, Ruth, and Tommy now as teenagers, residing in cottages on a farm in 1985. Although they are allowed to venture out occasionally, they grapple with the acceptance of their inevitable fates. At the farm, they encounter other former students of similar institutions, who reveal their shared identity as clones. Whispers of a potential "deferral" for couples in love circulate among them, igniting hope. Tommy becomes increasingly fixated on the notion that The Gallery was intended to scrutinize their souls, believing that their artworks could demonstrate the authenticity of their love. The evolving relationship between Tommy and Ruth grows intimate, and tension escalates, driving a wedge between Kathy and Ruth, ultimately resulting in Kathy's solitude as she embarks on a new role as a "carer." This position affords her temporary reprieve from donations as she comforts those who are facing their final moments.
The final act transports us ten years into the future, where Kathy continues her work as a carer, witnessing the demise of many clones as they surrender their organs. Upon reconnecting with a frail Ruth, who has endured two donations, they search for Tommy, who is equally frail. As they journey to the sea, Ruth confesses her insincere affection for Tommy, admitting that her seduction was born from her fear of loneliness. Burdened by guilt, she reveals her belief in the truth of the deferral claims and her discovery of Madame's address, who she hopes might help them. Tragically, Ruth passes away shortly after this revelation.
In the aftermath, Kathy and Tommy's relationship blossoms. However, their hope is soon dashed when they visit Madame, who, accompanied by Miss Emily, informs them that deferral is nothing more than a myth, and their artwork holds no sway over their fates. Instead, the purpose of The Gallery was to probe the ethical implications surrounding their existence, reflecting on whether the "almost human" clones possess souls at all. Devastated, the couple processes this devastating news, leading Tommy to explode with rage and grief, finding solace in their shared despair. The film culminates with Tommy succumbing on the operating table, leaving Kathy to confront her lonely future. As she reflects on the remnants of her childhood, she inevitably questions whether her destiny differs from those receiving her organs, asserting poignantly that, "we all complete."
