Maya and Bailey are abandoned by their parents. The parents divorce when the children are little and send their children to Stamps, Arkansas, to live with their grandmother (Momma). They travel alone and are stamped like baggage, a sad symbol that their parents view them as baggage. Even though Momma is able to care for them financially (she owns a store) and she loves them, they struggle with the abandonment throughout their lives. In Stamps, they face prejudice and racism. Maya grows up thinking she is ugly and stupid. Bailey sticks up for his sister as they grow up, but they both experience such things as being treated like second-class citizens, people assuming they are stupid and dirty, living in fear of lynch mobs, seeing their uncle almost caught by the KKK, having to endure indignities in church and in school, seeing their grandmother insulted by lewd acts by her neighbors and customers, etc.
One day, their father shows up and drops the children off with their mother, who is living with a man who rapes Maya. This results in a whole host of other problems for Maya, who becomes depressed and stops speaking to everyone except Bailey. She and Bailey return to Stamps after the trial of the boyfriend (Mr. Freeman), but then Momma sends them to California to live with their mother again to escape the increasingly dangerous racism in Arkansas.
This is a really brief summary, but you can read more about it here on eNotes.