While spending the summer with his grandparents, Oliver meets Mia, and the two immediately become the best of friends. Knowing Oliver would leave at the end of the summer, they promise to write each other.

But when Oliver decides to run away to go back to see her, a terrible accident causes him to lose the precious memories of his best friend. Years later, Oliver finds a picture of Mia, and becomes obsessed with finding his missing memories, and his childhood friend.

Mia has never forgotten Oliver, so she agrees to help him piece together the months he with his grandparents, all the while hoping he will remember her, and remember the promise they made to each other.