The Poet X by Elizabeth Acevedo is a novel written in short poems. The story is told from the first person point of view of Xiomara Batista through her sophomore year of high school. She lives with her twin brother Xavier and her parents in New York. Originally from the Dominican Republic, her mother once wanted to become a nun, although now she works as a cleaning woman, but she is still very religious. Xiomara's father was a womanizer until the twins were born. He works for the transit authority and doesn't interact much with his children. Although they are twins, Xavier is a junior because he is so smart. He attends a private school. Their best friend is Caridad whom they have known since they were babies.

Xiomara attends confirmation classes with Caridad, but she struggles with questions about God. She tries to talk to Father Sean, who seems like he might understand because he is young and once enjoyed boxing, but he doesn't provide Xiomara with many answers. Xiomara also loves to write. Her English teacher Ms. Galiano wants her to join the Poetry Club at school, but it meets on Tuesdays at the same time as her confirmation classes.

Xiomara meets a boy in Biology named Aman, and they begin hanging out at the smoke park and listening to music. He invites her to a Halloween party. Even though she is forbidden from dating, X sneaks out and goes to the party where she has a great time. Her brother and Caridad cover for her. On a day off, she and Aman go ice skating, and they make out on the train ride home. Her mother sees her and forces her to kneel on rice and pray to the Virgin Mary. She also takes away her phone. She and Aman stop talking and when a boy grabs her at school, Xiomara is angry with Aman for not defending her. She tells him to stay away.

Xiomara's mother returns her phone at Thanksgiving, but she has no one to call. She continues to write in her journal, and Father Sean suggests that perhaps she's not ready for confirmation. Xiomara takes the opportunity to begin attending the Poetry Club. She meets Isabelle who invites her to eat lunch with her in the photography room. For Christmas Xiomara's mom gives her a bracelet, and things seem to be improving. Unfortunately, Twin, whom she found out was gay, is dumped by his boyfriend Cody because he's moving away.

For her birthday in January, Xiomara receives tickets to an apple farm, which she knows were secretly delivered by Aman. Twin gives her a new journal to write her poems in. At school the next day, she realizes she left her old notebook at home, and when she returns, her mother has read it and sets in on fire. Stunned, Xiomara runs away. She texts Aman, and he brings her to his house where they get back together. After school the next day, she returns home with Caridad, Twin, and Father Sean supporting her to face her mother who cries and reconciles with Xiomara. They begin family counseling with Father Sean once a week.

Everyone goes to support Xiomara at the Poetry Slam, for which she has practiced for weeks. She does a great job, and they celebrate afterwards at her house. Xiomara realizes the power of her words and is pleased that her family is getting along.