In 1980, four-year-old Reyna Grande’s mother is preparing to leave Mexico for the United States—“El Otro Lado,” or “The Other Side,” as it is known in their impoverished city of Iguala. Reyna and her older siblings Mago and Carlos beg Mami not to leave, but she insists she must leave to join their father, who has already been working in the US for years in order to make money for their family. Mami drops the children off at the home of Abuela Evila—their father’s mother. Abuela Evila is not happy about looking after the children, and reminds Mami to send money every week.
Reyna, Mago, and Carlos suffer difficult and even abusive treatment at their Abuela Evila’s house. They sleep squished together on a straw mattress, are forced to eat table scraps, and are neglected by their grandmother even as she dotes on her other grandchild, Élida, whose own mother María Félix left years ago for the US. Reyna and her siblings endure lice and roundworm infestations, scorpion bites, as well as taunts from Élida and all the neighborhood kids about being “orphans.” When news arrives that Mami is going to have another baby, Reyna and her siblings grow even more despondent, convinced that their parents have forgotten all about them.
Nearly two years after leaving, Mami returns to Iguala—with her new daughter Betty in tow. She takes Reyna and her siblings to live with her at her own mother Abuelita Chinta’s house, and all of the children are delighted to have their mother back. As the days and weeks go by, however, they realize that the woman who has returned is not the same as the woman who left. Mami reveals that Papi left her for another woman, and her bitterness seeps into her relationship with her children. Mami soon takes up with a new boyfriend, and announces that she is moving away again, this time to Acapulco. In Mami’s absence, several tragedies befall their family. Reyna’s cousin Catalina is drowned in a horrible flood, and Betty is burned terribly when Abuelita Chinta spills boiling water on her face. One day, a neighbor arrives with news that Mami has called: after a horrible car accident that killed her boyfriend, Mami is coming home at last. When she returns, Mami is manic and reckless and eventually announces that she is moving to the other side of town to live with her sister, Tia Güera.
One day, Reyna and her siblings excitedly head over to Abuela Evila’s house to take what they think is a phone call from Papi. When they get there, though, they find their father—gone for nearly four years—sitting on the sofa with his new girlfriend, Mila. The reunion is awkward, but soon Reyna and her siblings are overjoyed, thinking their father will stay. The next day, Papi announces that he is returning to El Otro Lado soon—and plans to take Mago with him. Reyna and Carlos protest, begging to be brought along as well. Mami agrees to let the children go—but demands that Betty stay behind in Iguala. After two unsuccessful and dangerous attempts to cross the border, Reyna, her siblings, and their Papi at last make it to the US on their third try.
In September of 1986, Reyna, Mago and Carlos are preparing to start school in Los Angeles. Papi tells them that his expectations are high—he has risked a lot to bring them to this country, and tells them that if they do not succeed in school and take advantage of every opportunity afforded to them, he will send them back to Mexico. Papi soon begins abusing the children—when Carlos wets the bed, he throws him into a freezing tub of water. When Reyna refuses to spaghetti because it reminds her of the roundworms she had back in Mexico, Papi dumps the plate over her head and screams at her. When Mago gets her period for the first time and misses school because of her cramps, Papi lashes her with a belt. Mila turns a blind eye and offers Reyna and her siblings little comfort.
One day, Papi takes a bus downtown and returns with shocking: Mami is living just on the other side of town. More than that, she has come here with her boyfriend, has left Betty behind in Mexico, and is pregnant. Reyna and her siblings are desperate to see their mother, but Papi is enraged that they’d want to see a woman who moved to the same city as them and didn’t even contact them. Papi forbids them to see their mother until several months later, when Betty arrives in the US. When Reyna and her siblings take a bus to Mami’s new neighborhood, they are struck by how dangerous and impoverished it is. Mami’s new apartment is dirty and vermin-ridden, and yet Mami says that nothing can compare to the poverty she left behind in Mexico. Reyna and her siblings begin visiting Mami every weekend, but Reyna can’t help but notice that even though the physical distance between them all has closed, there are still major gaps to cross.
Mago starts high school, and Papi is proud of her for being the first person in their family to do so. Reyna becomes jealous, knowing that even if she succeeds and lives up to all of Papi’s expectations, she will never be the first to do so. She seeks out other ways to set herself apart from her sister, and takes up the alto saxophone both as a way of impressing Papi and as a method of expressing herself—English is still hard for her, but when it comes to the sax, there is only music. Papi decides to start taking English language classes himself, hopeful that once he gets a green card and learns English he’ll be able to move his family out of their gang-ridden neighborhood. When Papi learns that his sister, Emperatriz, has moved into the property he owned back in Iguala, he returns to Mexico to get it back, risking his green card process. When Papi returns, he still hasn’t been able to get his property back, and Reyna notices that something within him seems to have broken—he stops going to English classes, and starts drinking heavily.
As Mago graduates from high school, Reyna and her siblings at last obtain their green cards. Reyna joins marching band while Mago heads off to college, but Papi’s abuse is growing worse by the day. Mila tries to explain Papi’s abusive nature, claiming that he grew up in an abusive household, but Reyna is conflicted and unsure of what to believe. Mago gets fed up with Papi’s abuse, and looks for small ways to retaliate against his influence. She throws Reyna a quinceañera all by herself—though Reyna knows Mago is sliding into credit card debt, she is grateful for the party. Reyna is succeeding in school and band, but Papi hardly seems to notice all her accomplishments. Reyna leans on Mago as she struggles with boy problems and feelings of worthlessness, and in 1993, during Reyna’s senior year of high school, the two of them, along with Mami and Betty, take a trip back to Mexico. Reyna is shocked to see how Iguala has deteriorated, and as she reconnects with her family and friends, struggles to believe that she, too, grew up in such poverty. Mago dismisses Reyna’s attempts to reconnect with the past, and wants to go off to Acapulco to party. The two sisters get into their first big fight as they hash out feelings of obligation and disconnection to their Mexican heritage.
When Mago and Reyna return to Los Angeles, Mago begins looking for an apartment with some friends. She tells Reyna that she will be able to come live with them, too, and finally escape Papi’s abuse. A few weeks later, though, when Mago secures an apartment, she revokes her offer to Reyna. When Mago tells Papi that she’s moving out, he tells Mago she’ll be dead to him if she goes through with it. Though things are stony and silent for a few days, Mago sticks around, and Reyna wonders if perhaps her sister won’t go after all. Reyna is accepted to UC Irvine, and they all go out to celebrate—but the next day, Mago moves out without a word, and Papi tells Reyna she is forbidden from going to school. Papi’s drinking worsens, and Reyna is subjected to frequent beatings. Reyna begins holing up in her room, refusing to come out while Papi is home. She engages in reckless behaviors, starting to have unprotected sex with her boyfriend Steve and getting into a dangerous situation with two men who offer her a modeling gig. At rock bottom, Reyna decides to turn herself around. She breaks up with Steve and announces to Papi that she’s enrolling in community college. She is expecting a fight or even a beating, but Papi accepts her decision.
Reyna enrolls at Pasadena City College and meets her first mentor, a professor named Diana Savas, who introduces Reyna to many great books from the Latina literary canon. Even after Dr. Savas’s class is over, Reyna continues going to see her professor to talk about books and literature. One night, Papi pushes Mila down the stairs and is arrested. Reyna goes to stay with Mami, but realizes she cannot live in such cramped, dirty conditions. Reyna confesses the truth about her abusive home life to Dr. Savas, who invites Reyna to come and live with her. Reyna accepts. A year and a half later—after having returned to him for a while—Mila decides to leave Papi, taking money from their bank account and filing a restraining order. Papi is left with nothing, and both Mago and Carlos—who are busy with their own families and children—encourage Reyna to move home for the summer before she starts classes at UC Santa Cruz, to care for Papi. Reyna reluctantly agrees, and finds that Papi is more docile, friendly, and present than he has ever been. At the end of the summer, Papi makes an announcement: Mila has decided to move back in, on the condition Papi cuts off all contact with Reyna and her siblings. Stunned and hurt, Reyna packs her bags, and stays with Dr. Savas for the last few days of her summer vacation. Reyna’s boyfriend Edwin drives her up to UC Santa Cruz several days later, and tries to remind her that Papi probably didn’t want to hold Reyna back any more—he knew she’d be leaving anyway, and didn’t want to be alone. After her boyfriend drops her off at school, Reyna decides to “let go” of her anger towards Papi and start fresh.
In an epilogue, Reyna reveals that she went onto become the first person in her family to graduate college. She worked as a teacher for many years before devoting herself to writing; her first two novels were highly acclaimed, and she soon began attending lectures, conferences, and parties with the Latina writers she’d once admired as a fan. She repaired her relationships with Mila, Papi, and her siblings over the years, and became a US citizen. In 2010, Papi was diagnosed with liver cancer. Though her siblings sometimes felt that Papi was finally getting what he deserved, Reyna stood by her father’s side throughout his illness, pushing aside her feelings of anger and regret in order to be present for him in his final days. In the end, as Reyna and her siblings allow their father’s doctor to take him off life support, Reyna holds her father’s hand and realizes, for the first time, that it is the same shape as hers. She wonders to herself whether she would have come with him to El Otro Lado if she knew all she’d suffer here—as Papi takes his last breaths, she decides that the answer, despite it all, is “yes.”