Eleanor and Park opens with Park thinking about Eleanor and how he can't bring her back. Then it flashes back to the past and Park on the bus thinking about music and interacting with Steve and Tina, two bullies who attend school with him. When a new girl gets on the bus and people refuse to sit with her, Park lets her sit with him despite his reservations.
The girl on the bus, Eleanor, begins to sit next to Park regularly. They talk about music and comic books; during their discussions, they learn that they have a lot in common. Eleanor's home life is very unhappy. She lives with her mother, siblings, and abusive stepfather, Richie. Her mother tries to hurry the kids out of the common areas before Richie gets home.
As Eleanor gets more comfortable at school and with Park, she gets frightening, sexual messages written in her textbooks. At home, she listens to her mother crying while Richie screams at her. She lives in fear of her or her siblings upsetting Richie. Meanwhile, Park gets closer to his parents as they begin to accept things about him that they don't like. For example, he wears eyeliner. Park's parents also grow to like and care for Eleanor.
Ultimately, Park falls in love with Eleanor. She seems to love him too, though she can't make herself say it back. When she goes home to find her things destroyed and realizes Richie not only ruined them but also has been leaving her obscene notes, she realizes she's not safe. She finds out he's been out looking for her. Steve and Tina help her escape the house, and Park drives her to her extended family so she can live somewhere safe.
While they're apart, they both think about each other. Park writes to her, but she doesn't respond, because she decided that they were just going to stop if they couldn't be together forever. His parents tell him it appears that Eleanor's mother took the kids and left Richie. He gets a postcard the day after prom from Eleanor that is only three words long, and it appears that Park feels hope for the future.