Lara Jean has never openly admitted her crushes. Instead, she wrote each boy a letter about how she felt, sealed it, and hid it in a box under her bed. But one day Lara Jean discovers that somehow her secret box of letters has been mailed, causing all her crushes from her past to confront her about the letters: her first kiss, the boy from summer camp, even her sister's ex-boyfriend, Josh. As she learns to deal with her past loves face to face, Lara...

As high school ends, Lara Jean looks forward to her father's remarriage and seeing her sister, but she must choose a college, prepare to leave home, and possibly leave her beloved Peter behind.