Margot Song leaves to go to Scottland for collage. Before she leaves, though, she breaks up with Josh, her boyfriend.
Lara Jean Song keeps a hat box in her closet. Her mother gave it to her before she died. In her hat box she keeps her deepest secrets. Including the love letters that she writes to boys when she doesn't like them anymore. She wrote the addresses and everything on the envlopes.
One day at school after she had a fight with her younger sister, Kitty, Peter comes up and asked her why she sent him a love letter. Lara Jean freaks out because someone sent her letters and they were not meant to be sent. She assures Peter that there is no meaning to the letter. She had wrote five letters. Did all the boys get their letter that they were never supposed to get?
One day while she is at her locker and Josh comes up and shows her the letter. She says that it means nothing even though she still kind of likes him. She then sees Peter and runs up to him and hugs him. She make up a story on how she and Peter are dating.
After school she goes over to Peters house to talk about what their story is going to be about thir fake dating. They come up with a "contract," about the things they can or can't do. They went to parties and even a ski trip together. At the ski trip they end up falling in love.
At Lara Jeans Chistmas party, Josh gets mad at Peter because he thinks that he is just using Lara Jean. They end up in a big fight and she tells Peter and Josh both to leave. She then realizes that she is in love with Peter and writes another letter to him saying that she is very sorry.