If you know nothing of the story's premise, I'm saying nothing to spoil the film by saying it is about a possible dystopic future where humans have discovered the ability to clone a subset of humans, which
they raise in schools across the country, educate them about the proper use of their bodies and health, but eventually use them to harvest their vital organs to defer the life spans of other, "real" humans. Death and disease are gone. At the expense of other "lives."
The premise is fodder for dozens of similar clone sci-fi films, but Ishiguro's novel brought to the table the basic question of what it means to be human and what it means when we consider a particular subset of human, un-human.