She impulsively drives back to the lake house, finds Alex's letter and writes back.Both Alex and Kate continue passing messages to each other via the mailbox, and each watches its flag go up and down as the message leaves and the reply arrives as they wait at the mailbox.
Kate goes to the restaurant but Alex fails to show.
They cautiously look around each time the flag changes, hoping to somehow spot the other. They then discover that they are living exactly two years apart.
Their correspondence takes them through several events, including Alex finding a book, Jane Austen's Persuasion, at a railway station where Kate said she would have lost it, and Alex taking Kate on a walking tour of his favorite places in Chicago via an annotated map that he leaves in the mailbox.
The two meet via letters left in a mailbox at the lake house they have both lived in at separate points in time; they carry on correspondence over two years, remaining separated by their original difference of two years.
This film reunites Reeves and Bullock for the first time since they co-starred in Speed in 1994. Kate Forrester (Sandra Bullock) is leaving a lake house that she has been renting in Madison, Wisconsin to move to Chicago.