Amir is a young boy in Kabul, Afghanistan, during the 1970s. He lives with his father, whom he calls "Baba,” and their servants, Ali and Hassan. Ali is one of Baba's oldest friends, but because he is Hazara, a race of Afghan descended from Moguls, he is considered lower class and must work as a servant. Hassan is Ali's son and Amir's closest friend. Because Hassan is also Hazara, he is not allowed to go to school with Amir and must work with Ali.
Amir spends most of his free time playing with Hassan and reading to him, but often plays tricks on his friend by making up the wrong endings to the stories. Although Amir loves Hassan and thinks of him more as a brother than a servant, he cannot help being jealous of him because of the way Baba also loves Hassan. Amir, who is desperate for his father's approval, doesn't understand why his father buys Hassan birthday presents or insists on taking him with them on family outings. Even though Amir sometimes treats him cruelly, Hassan always forgives Amir. Hassan stands up to the bullies who pick on them in the streets. One boy, Assef, vows to get his revenge on them after Hassan threatens him with a slingshot to stop him from beating Amir.
Each winter, all of Kabul celebrates a kite tournament. Boys and young men fly kites and try to cut each other's strings until one kite is left in the sky. Victory belongs not only to the boy who flies the remaining kite, but also to the boy who retrieves the last kite to fall. Amir and Hassan have practiced as a team for years — Amir flying the kite, and Hassan holding the string and running after the fallen ones. When Amir is 12 years old, and Hassan 11, they vow to win both prizes in the tournament. Amir believes his victory will finally make his father proud of him.
The day of the tournament arrives, and Amir is terrified he will fail. Hassan gives him the courage to fly the kite. The two work together, Hassan holding the string, Amir pulling it to dance in the sky and fight with the other kites. At the end of the day, Amir's is the only kite flying. Hassan runs through the streets, promising to retrieve the last fallen kite so Amir's victory will be complete. Amir winds his kite in, then searches for Hassan. He finds his friend trapped by Assef and two other boys. Hassan has found the kite, but Assef wants it. When Hassan refuses to trade the kite for his freedom, the boys attack and rape him. Amir watches from the shadows, wishing he had the courage to help his friend. Instead, he runs away before the boys and Hassan see him.
Amir's guilt at having let Hassan be sodomized destroys their friendship. He cannot look at Hassan without remembering all his friend did in order to get the kite. His guilty conscience eats away at him. After his 13th birthday party, Amir plants money and a watch in Hassan's house in order to frame him for stealing. Baba questions Hassan, who admits to the theft, even though he is innocent. Although Baba has always said that stealing is the worst crime a man can commit, he is willing to forgive Hassan. Ali steps forward and tells Baba that he and Hassan are leaving. For the first time in his life, Amir sees his father cry. Baba begs Ali to stay, but Ali refuses. The servant looks at Amir, and the boy knows that Hassan has told him everything — about the rape, about Amir's rejection of him and about him framing Hassan for the theft. It is the last time Amir will see his friend alive.
Five years later, Baba and Amir escape from the Russian takeover of Afghanistan by smuggling themselves out of Kabul in an empty fuel truck. Eventually they travel to America and settle in California. Baba works as a mechanic while Amir finishes high school and starts junior college to study English so he can become a writer. Before Baba dies of cancer, Amir meets and marries Soraya, a young woman also from Afghanistan. Amir becomes a writer while Soraya becomes a teacher. The two are happy, even though Amir is never able to forget the sins he committed as a child. When he and his wife are unable to have children, he believes it is a punishment for what he did.
In 2001 Amir receives a phone call from his father's old business partner, Rahim Khan. Khan had also been Amir's confidant and had encouraged Amir to write. Although Amir never told Rahim Khan what he did, he suspects the man knows. Khan tells Amir that he is dying and wishes to see him one more time. Before hanging up, he suggests that there is a way Amir can redeem himself.
Amir flies to Pakistan to meet with Rahim Khan. Rahim tells Amir of the horrendous state of Afghanistan since the war with Russia and the Taliban takeover in 1996. He fills Amir in on all that has happened to his friend Hassan, including his and his wife's murders at the hands of Taliban officials. Khan then begs Amir to return to Afghanistan to bring Hassan's son, Sohrab, to Pakistan. When Amir initially balks at the request, Khan tells him the truth about Hassan's parentage: he was Amir's half-brother, Baba's son.
Amir agrees to try and retrieve his nephew from an orphanage in Kabul. The journey is treacherous, and Amir is shocked by the scars left from the war with Russia and the brutality of Taliban rule. When Amir finally locates the orphanage that housed Sohrab, he learns the boy has been sold to a Taliban officer. Amir arranges a meeting to see if he can buy the boy's freedom. The Taliban officer turns out to be Assef, the childhood bully who'd raped Hassan. Assef is molesting Sohrab. When Amir offers to buy the boy, Assef refuses. He beats Amir almost to death, and it is only when Sohrab manages to shoot Assef's eye with a slingshot that the two escape.
It takes many weeks for Amir to recover from his injuries, during which he asks Sohrab if he would like to live with him in America. Although afraid to leave his country, Sohrab is more afraid of having to return to an orphanage. He agrees to go with Amir, but government red tape holds up the process. When Amir tells Sohrab he may have to return to an orphanage just until they can get all the paperwork cleared, the boy tries to commit suicide. Amir remains with Sohrab until he is able to travel and then brings him to California. Though Sohrab survived the suicide, he has become a mute, psychologically unable to speak to anyone. Many months later, Sohrab still has not spoken or smiled. Amir and Soraya take him to the park where fellow Afghans celebrate the Afghan new year. Sohrab notices some kites flying, something he used to do with his father. After Amir manages to win a fight with another kite, Sohrab smiles. It is a small step, but one Amir hopes will blossom into healing.