This is the opening scene when the narrator finds out his brother has been arrested for selling Heroin. In his algerbra class he comes to the realization, that his students could end up like his brother oneday.
On the narrator's way home from work he runs into one of his brother's friends. Sonny's is his brother. Sonny's friend tells the narrator about Sonny's drug habits and issues.
After the death of the narrators daughter, grace. he begins to write letters to Sonny in prison. Sonny responds to the letters and tries to explain to the narrator how he ended up in prison. Sonny is released from prison. His brother the narrator is there to pick him up.
In a flashback the narrator remembers that Sonny and their dad used to fight a lot because they were so similar. He also remembers telling his mother he would take care his brother. The narrator doesn't think about his brothet until their mothers funeral.
Take care of your brother
After the funeral, Sonny and the narrator start living together. Sonny tries to explain to his brother that he wants to be a musician. The narrator doesn't support his decision. After they get into a fight about Sonny missing school and spending all his time on music, Sonny decides to leave and join the Marines.
Once Sonny is out of prison for a few weeks, he takes his brother to a night club he is well known at. Sonny performs for his brother. The narrator comes to the realization that music is very important to Sonny. He decides to support his brothers dream of music.