I have included links below to more information about this novel on the enotes study guide section of this site, and you will find in particular a very detailed summary, but here is a much more concise version.
This novel tells the story of two women in Afghanistan, and in particular how their lives intersect. Mariam is a woman who grew up as an illegitimate child, her mother having been seduced by her employer. When Mariam demands recognition, her father ignores her and her mother commits suicide. Her father then marries her off to a man much older than her, called Rasheed, who is a strict Muslim and insists that Mariam wear the full burqa and live an isolated life.
Meanwhile, nine-year-old Laila's youthful love for Tariq, a local boy, is described. Laila's family are about to leave Kabul because of the fighting and the civil war, and so the two are separated. However, Laila's parents are both killed by a rocket attack, leaving her by herself and isolated in Kabul. She goes to Rasheed and he takes her as his second wife.
Rasheed beats Mariam but not Laila. Laila quickly has one child and then another a little later who are very different. Finally it becomes clear that Laila's first child's father was not Rasheed but Tariq, and Rasheed becomes violent towards them both. Finally, Mariam protects Laila by hitting Rasheed, killing him. Laila runs away with Tariq to make a new life together in Pakistan while Mariam is stoned publicly in a football stadium for killing her husband.