In an alternate version of England in the late 20th century, a trio of young students—Kathy, Tommy, and Ruth—progress through their childhood at Hailsham, a seemingly idyllic but mysterious boarding school. The children are sheltered from the outside world and are brought up under strict and peculiar rules that emphasize the importance of their health and well-being above all else. The school is run by the authoritative Miss Emily and the caring yet enigmatic Miss Lucy, who both enforce the institution's cryptic doctrine. The students are taught they are special, without fully understanding the true purpose behind their upbringing.

Kathy develops a deep bond with Tommy, but their burgeoning friendship is complicated when Ruth, the more assertive of the trio, also takes an interest in him, forming a love triangle that persists into their teenage years. As they grow older, they begin to grasp the grim reality of their existence and the role they are expected to play in society. Their coming-of-age journey forces them to confront emotions of love, jealousy, and betrayal, while wrestling with profound existential questions about their destiny and the moral implications of their predetermined fate in a world that values them for a singular, haunting purpose.