Lara Jean has never openly admitted her crushes, but she's written each boy a letter about how she felt, and sealed it, and hid it in a hatbox under her bed. One day she finds that her secret box of letters has been mailed, and her life goes out of control.

It is 1960. When Jennifer Stirling wakes up in the hospital, she can remember nothing--not the tragic car accident that put her there, not her husband, not even who she is. She feels like a stranger in her own life until she stumbles upon an impassioned letter, signed simply "B," asking her to leave her husband. Years later, in 2003, a journalist named Ellie discovers the same enigmatic letter in a forgotten file in her newspaper's archives. She becomes...