The lake house

Kate Forster is a Doctor in 2006, living alone in Chicago. She has moved into an apartment after living in a house built next to a scenic lake in a secluded countryside area. She writes a letter to the next tenant asking that they forward any mail, and that the paw prints and the box in the attic have always been there. The tenant Alex Wyler reads the letter, but finds no paw prints, no box and no sign of life within the last 5 years, so disregards the letter until a few days later when he is redoing the paint on the handrails and a stray dog, whom Alex takes in and names Jack although the dog is female, trots through the brown paint and leaves its paw prints all the way to the front door. He writes to Kate asking more about these incidents and leaves the letter in the mail box.
On Valentine's Day 2006, Kate visits the Lake House after having a gentleman die in her arms after being hit by a bus, but finds the Mail Box Flag is up. She reads Alex's letter and states her current address, also stating it is 2006, not 2004 from which Alex's letter arrives from. Alex attends her 'current address' but finds a construction site that won't be finished for another 18 months, and they both slowly realize they are communicating from two years apart, with only the Mailbox to communicate from.
As Kate and Alex continue to correspond through the mailbox, they find themselves falling in love. Because Kate is in the future, she can tell Alex specific places to look for her in 2004. On one occasion, she asks Alex to bring her back something important (a gift from her father; her favorite novel by Jane Austen called Persuasion), which she left two years ago during a train station meeting with her then-beau, Morgan. Alex goes to the station and finds the item and sees Kate with long hair. Even though he has the item, he does not place it in the mailbox to return it to her. Instead, he says that he will return it to her personally, "one way or the other." Alex sends her a personalized map of Chicago and takes her on a walking tour of his favorite places in the city one Saturday morning. He leaves her a loving message on a brick wall at the end written in 2004, that she sees in 2006. The message was "Kate, I am here with you. thank you for spending this Saturday together".
In 2004, Mona, a young attractive assistant, is flirting with Alex but he ignores her advances. Alex's dog Jack runs off and leads Alex to a house in which Morgan and Kate are currently living. Alex talks with Morgan and eventually is invited to the birthday party Morgan is holding for Kate that evening. During the party, Alex and Kate dance together and share a romantic kiss, which is broken up by Morgan and Mona. Later, Kate and Alex discuss that night and Kate announces she liked him, and can remember what he looks like.
Crisis enters Alex's life when his estranged father has a heart attack and shortly thereafter dies. Kate somehow discovers his death certificate at the time he dies. She rushes to the mailbox and as a gift to Alex, she places a book in the mailbox, which she says is a tribute to his father, a book that is not yet published in Alex's time.
Determined to bridge the distance between them at last and unravel the mystery behind their extraordinary connection, they tempt fate by arranging to meet. Alex makes a reservation in 2004 for a date in 2006 at Il Mare, a fancy restaurant, but only Kate appears. Alex does not show up. The next day Kate writes Alex a letter telling Alex of this fact, but he doesn't understand. "Something must have happened" he responds. Kate retreats, believing she will never have happiness. She urges Alex to move on She tells him about Valentine's Day 2006 when a man died "in her arms", and that she needs to live her own life. She asks Alex not to contact her again. Alex leaves her a growing pile of letters in the mailbox that she never retrieves. He is brokenhearted and decides to leave the lake house. He places the box in the attic that Kate referred to in her first letter.
Alex appears to Morgan and hands him the keys to the lake house and exits in his truck, leaving Jack behind and having her become Kate's dog.
Almost one year passes.
In December 2007 Kate and Morgan are apparently living together in a Chicago apartment and when he asks her to turn the film she is watching down, she switches it off and storms into the bedroom where a squeaky floorboard irritates her, so she rips it out and discovers her copy of Persuasion, with a pressed and faded rose marks a passage that Kate is particularly touched by. She realizes she still loves Alex, but does not contact him.
On Valentine's Day 2008, Kate and Morgan go to Visionary Vanguard Associates, an upcoming architect's office, to talk about renovations to the apartment they are living in at that time, but do not realize it is run by Alex's brother Harry. Kate notices a beautiful watercolor of the Lake House and asks who did it. Harry says it was done by Alex Wyler, his brother, but tells her he passed away 2 years ago to the day. Kate realizes something and sprints to her car and races to the mailbox by the Lake House, placing a letter inside. Alex was the man that died that day, two years previously, and she tells him to wait 2 years, not to look for her or try to find her. Kate knows that Alex can't change her reality what has happened in Kate's reality has happened. In order for Kate's and Alex's reality to merge, Alex must meet Kate at the Lake House on February 14th 2008.
In 2006, Alex watches as Kate has lunch with her mother, and makes to step off the curb, then watches as the bus that was going to hit him passes by instead. He smiles to himself and, instead of crossing the street, walks away from Kate.
In 2008, the Mail Box Flag squeakily drops and Kate, previously sobbing on the ground, watches it in earnest, and behind her a truck pulls up. Out steps Alex. They share their second passionate embrace and after several minutes walk arm in arm into the Lake House. Alex hands to her, what appears to be, a Valentine's Day card.