Normal People begins in the fictional town of Carricklea, in Ireland's rural county Sligo. There, a boy named Connell regularly drives to pick up his mother, Lorraine, from his job as a cleaner. Lorraine works in a mansion owned by the wealthy, odd Sheridan family. The Sheridans' daughter, Marianne, is in Connell's class at school. She is academically brilliant but friendless and bullied, especially by Connell's popular friends. Connell and Marianne begin to casually talk when Connell goes to pick up his mother, and their small talk soon escalates to a romance. Marianne even encourages Connell to apply, like her, to the prestigious Trinity College. However, Connell, not eager to be associated with Marianne at school, insists on keeping their relationship a secret. Eventually, when he asks another girl to a dance, Marianne becomes upset and stops speaking to him.
They reunite in college, where their roles have reversed and Marianne is considered popular but Connell feels out of place. Soon, they begin having sex again, and their feelings for each other deepen. They are happy together, but their relationship once again crumbles, this time because Connell cannot afford rent for the summer. Ashamed to ask Marianne for a place to stay, he returns home to Carricklea, leaving her hurt and bewildered. While Connell is home for the summer, he runs into an old teacher Paula Neary, who tries to make him have sex with her while he is drunk.
When Connell and Marianne reunite, Connell tells Marianne about his encounter with Paula. Marianne tells him about her new boyfriend, Jamie. Jamie is cruel and pretentious, and behaves sadistically towards Marianne—sometimes because she asks him to, but often unprompted. This is especially distressing for Marianne because she comes from an abusive family—a fact of which Connell is only dimly aware, since she avoids telling him about it. Soon after, Connell calls Marianne for help while she has Jamie and various other friends gathered in her apartment. He tells her that he has been mugged and has no phone or money. When he arrives at Marianne's, he gets into a small but dramatic argument with Jamie. Afterward, he tells Marianne that he has a new girlfriend named Helen; Marianne is upset, though she tries not to make Connell feel guilty.
Connell and Marianne are both awarded large scholarships, so over the summer, Connell uses his to travel Europe with friends. During this period, he works on his writing, a passion of his. Connell and his friends briefly stop over at Marianne's family's vacation home in Italy, where she is staying with Jamie and her friend Peggy. Tensions between Jamie and Marianne escalate into a vicious fight, and Marianne spends the night in Connell's bed. She tells him about her abusive family. They kiss, but Marianne stops Connell from continuing. Soon after, she goes to Sweden, where she is studying for the academic year.
In Sweden, Marianne's mental health declines: after breaking up with Jamie, most of her friends have abandoned her. She has developed an eating disorder and she seeks out men who will physically hurt her when they have sex, such as a Swedish photographer named Lukas. Meanwhile, in Dublin, Connell learns that his high school friend Rob has committed suicide. This sends him spiraling into a deep depression. It also causes him to break up with his girlfriend Helen. The only things that help Connell are working on his writing and Skype calls with Marianne in Sweden.
The following summer, Marianne and Connell spend time together in Carricklea. They discuss getting back together and start to have sex, but when Marianne asks Connell to hit her and he refuses, she leaves, feeling rejected and ashamed. When she goes back to her family's house, however, her brother physically attacks her. She calls Connell for help, and he comes to pick her up, confronting her brother before he leaves. When we next see Marianne and Connell, they are happily together in Dublin. But Connell learns that he has been admitted into a creative writing graduate program in New York, and Marianne encourages him to go, knowing that, while they will have to be apart, they have already given one another a great deal of help.
