Solène Marchand, the thirty-nine-year-old owner of an art gallery in Los Angeles, is reluctant to take her daughter, Isabelle, to meet her favorite boy band. But since her divorce, she's more eager than ever to be close to Isabelle. The last thing Solène expects is to make a connection with one of the members of the world-famous August Moon. But Hayes Campbell is clever, winning, confident, and posh, and the attraction is immediate. That he is all of twenty years old further complicates things. What begins as a series of clandestine trysts quickly evolves into a passionate relationship.

Connell and Marianne grew up in the same small town, but the similarities end there. At school, Connell is popular and well liked, while Marianne is a loner. But when the two strike up a conversation - awkward but electrifying - something life changing begins. A year later, they’re both studying at Trinity College in Dublin. Marianne has found her feet in a new social world while Connell hangs at the sidelines, shy and uncertain. Throughout their years at university, Marianne and Connell circle one another.

Michael is coming undone. Adrift after his wife's departure, he has begun taking himself on long, solitary walks across the English countryside. Becoming ever more reclusive, he’ll do anything to avoid his empty house. Marnie, on the other hand, is stuck. Hiding alone in her London flat, she avoids old friends and any reminders of her rotten, selfish ex-husband. Curled up with a good book, she’s battling the long afternoons of a life that feels like it’s passing her by.

Sixteen-year-old Lara Jean Song keeps her love letters in a hatbox her mother gave her. They aren’t love letters that anyone else wrote for her; these are ones she’s written. One for every boy she’s ever loved - five in all. When she writes, she pours out her heart and soul and says all the things she would never say in real life, because her letters are for her eyes only. Until the day her secret letters are mailed, and suddenly, Lara Jean’s love life goes from imaginary to out of control.

Eve, Justin, Susie, and Ed have been friends since they were teenagers. Now in their thirties, the four are as close as ever, Thursday night bar trivia is sacred, and Eve is still secretly in love with Ed. Maybe she should have moved on by now, but she can’t stop thinking about what could have been. And she knows Ed still thinks about it, too. But then, in an instant, their lives are changed forever.