Set in the U.S. in an unspecified future, the book is told from the point of view of Klara, a solar-powered AF (Artificial Friend), who is chosen by Josie, a sickly child, to be her companion.

Klara comes to fear and hate what she calls the "Cootings Machine" (from the name printed on its side) which stands for several days in the street outside, spewing out pollution that entirely blocks the Sun's rays.

From Josie's bedroom Klara has a good view of the Sun's progress across the sky, and comes to believe that he goes to his nightly rest within a farmer's barn that stands on the horizon.

Although surprised to find the Sun's resting place is not actually in the barn, she pleads with him to pour his special kind of nourishment onto Josie and to save her life, as he did the beggar.

The mother regularly takes Josie to sit for her portrait, although unknown to her daughter the artist is making not a painting but a highly-accurate AF body.

When Klara next accompanies Josie into town, she finds and destroys a Cootings Machine, sacrificing in the process some of the P-E-G Nine solution she carries in her head and accepting that the loss may result in a reduction in her abilities.

Several days later as Josie seems near death Klara suddenly sees the dark clouds part, and the Sun sends his special nourishment flooding into her sick room.

Klara worries that she has misled the Sun and Rick comforts her, explaining that although his and Josie's paths in life may differ, their love really was genuine and they will always, at some level, be together.

Klara, the NY Times Book Review writes, "strikes the quintessential Ishiguro chord" when she says, "I have my memories to go through and place in the right order".

"[10] Publishers Weekly praised the "rich inner reflections" of Ishiguro's protagonist, writing, "Klara's quiet but astute observations of human nature land with profound gravity."

"[11] In her review for The New York Times, Radhika Jones said that Klara and the Sun returns to the theme of The Remains of the Day as "Ishiguro gives voice to: not the human, but the clone; not the lord, but the servant.

[13] The Economist praised the book, stating that it effects "a cross between Never Let Me Go and The Remains of the Day, with Klara in the place of Stevens, the butler whose first-person narration provided a between-the-lines portrait of morality among the English upper crust in the interwar years.

"[14] Anne Enright, writing in The Guardian, found parallels with a different work by the author: "The themes of replication and authenticity are similar to those in Kazuo Ishiguro's Never Let Me Go, published in 2005.

Both also contain a secret moral shift: an advance in technology that has changed people's sense of what it is to be human, and the emotional punch of Klara, as with Never Let Me Go, comes from the fact that the central character doesn't know what is going on.

Singer Richard Walters noted the novel as the jumping off point for main idea of the album, and Attlas added that he felt it connected to many of the new ways that AI was becoming a part of people's lives during the pandemic and into the 2020s.