Oscar de León (nicknamed Oscar Wao, a bastardization of Oscar Wilde) is an overweight Dominican growing up in Paterson, New Jersey. Oscar desperately wants to be successful with women but, from a young age, is unable to find love, largely because he is a nerd obsessed with science fiction and comic books. His great fear is that he will die a virgin.
After high school, Oscar attends Rutgers University. After "getting dissed by a girl", he attempts to kill himself by drinking two bottles of liquor and jumping off the New Brunswick train bridge. His sister's boyfriend Yunior (the narrator of much of the novel) moves in with Oscar and tries to help him get in shape and become more "normal". After a fight with his sister, Oscar again gets drunk, walks onto a train bridge, and jumps. He survives the fall but is seriously injured.
Oscar recuperates and graduates from Rutgers. He substitute teaches at his former high school and dreams about writing an epic work of science fiction. Eventually, he moves to the Dominican Republic and falls helplessly in love with Ybon, a prostitute who lives near him. Ybon is kind to Oscar but rejects his frequent romantic overtures. Ybon's boyfriend, a violent police captain, becomes jealous of Oscar and sends two goons who kidnap Oscar, take him to the sugarcane fields, and beat him into a coma. Oscar's family takes him back to the United States to heal.
Oscar recovers from the beating, borrows money from Yunior, and returns to the Dominican Republic. He spends 27 days writing and stalking Ybon. She is horrified at first but softens and eventually has sex with Oscar. Ybon's boyfriend's goons then find Oscar, take him back to the sugarcane fields, and kill him.
Flashbacks and secondary narratives
The novel contains significant exposition on Oscar's family history. One section is a first person narrative from the perspective of Oscar's sister, Lola, explaining her struggles to get along with their headstrong mother, Beli. Subsequent sections detail Beli's backstory growing up as an orphan in the Dominican Republic after her father was imprisoned and her mother and two sisters died.