I Know Why the Caged Bird Sings opens in 1931 as three-year-old Marguerite Johnson (nicknamed Maya) and her four-year-old brother, Bailey, arrive in the small country town of Stamps, Arkansas. Their recently divorced parents put the siblings on a train in California and sent them to live with their grandmother, Momma Henderson. Momma runs the general store in the African American section of Stamps, with the help of her disabled son, Uncle Willie. Maya doesn't understand why her parents have sent her away and has a vague sense she's done something to offend them. Growing up under the strict but caring supervision of Momma, Maya copes with feelings of abandonment, self-doubt, and lack of confidence. Her protective and supportive older brother Bailey becomes her best friend. More adventurous and more mischievous than Maya, Bailey shares her passionate love of books, and they spend endless hours reading, memorizing, and talking about the books that feed their vivid imaginations.
In highly segregated Stamps, Maya becomes aware of the divide between whites and African Americans. She resents the unfair restrictive social codes. She's angry and upset that Momma, for whom she has much respect, must behave in subservient ways toward whites.
After four years with Momma in Stamps, Maya and Bailey are taken to St. Louis to live with their lively, glamorous mother, who works in gambling parlors. When the eight-year-old Maya is sexually abused and raped by her mother's boyfriend, he is subsequently murdered, and the confusion and shock of the experience sends Maya into withdrawal and silence. Maya and Bailey are sent back to Stamps. Maya slowly recovers, with the help of Momma and the gentle, highly educated Mrs. Flowers (who connects with Maya through their shared love of literature) who manages to pull her out of her withdrawal. Maya becomes more and more aware of the ways in which deep-seated prejudice and hatred threaten both the livelihood and lives of African Americans in her community.
Her own direct experiences with racism, such as when a white dentist refuses to treat her and when a white employer decides to give her a new name, serve to increase her hostility toward all whites. While in many ways Maya identifies more and more with her African American community, she's critical of and can't identify with their acceptance of the status quo. During these years in Stamps, Maya makes her first friend, Louise, who helps her appreciate the joys of childhood. By the time Maya graduates from the eighth grade, she's feeling more self-confident and has made good progress on the road to self-acceptance.
Maya is 13 when she and Bailey go to live with their mother in San Francisco. Their father is also living in California, near Los Angeles. Vivian has remarried, and Maya's new stepfather, Daddy Clidell, becomes the first real father figure in her life. In wartime San Francisco, with its atmosphere of change and its new African American community, Maya finally finds a place where she feels at home. Her father, Daddy Bailey, who has been a virtual stranger in her life, invites her to spend the summer with him in southern California. Maya discovers her father is nothing like the fantasy she has built up. Conceited and self-centered, he shows no real interest in Maya. After his girlfriend physically attacks Maya, Maya decides to leave and ends up living with homeless teenagers in a junkyard. This turns out to be an unexpectedly positive experience for Maya. For the first time she finds herself in an environment where she feels accepted. The teens, who are African American, white, and Hispanic, work together, following rules they have set for themselves, to support each other through odd jobs. After a month in the junkyard, Maya goes home to San Francisco, having acquired an attitude of tolerance and also a new level of self-confidence.
Life in San Francisco seems a bit flat. Bailey has begun to spend time with a tough crowd, and he and Maya grow apart. Wanting distraction, Maya decides she needs to take a break from school and work as a streetcar conductor. There's a policy of not hiring African American females to work on streetcars, and the idea of challenging this racist policy appeals to Maya. With her mother's support and encouragement, Maya pursues the job. Her persistence pays off, and at age 15 she becomes the first African American female streetcar conductor in San Francisco.
Maya goes back to school after working on the streetcars for three months. Maya is just eight months away from graduating from high school when a one-time sexual encounter leaves her pregnant. Following Bailey's advice, she hides her pregnancy in order to stay in school and get her diploma. Once she graduates, she tells her mother and stepfather, who react with unwavering support. Just weeks after her graduation, Maya gives birth to a son and is both frightened and delighted as she enters into her new role as a mother.