Ronnie (short for Veronica) and Jonah's parents got divorced when they were young and they've been living with their mom. She is re-marrying a new man soon.
The mom decides to ship them off to their dad's for the summer since they haven't seen him since he left them, probably because their dad is dying of lung cancer and wants to make amends before he dies.
While there, Ronnie falls in love with Will, makes up with her father, breaks up with Will, gets back with Will and grows up from a surly teenage delinquent who doesn't know what she wants to do with her life into a strong compassionate young woman who finds purpose in her life.
Ronnie stays to take care of her ailing father and helps him write the last song he will ever write.
Before Ronnie's dad dies, Ronnie tells him of her decision to attend Julliard to study music which is conveniently located near Columbia where Will goes to school.