Feeling that it's time for a change in her life, Dr. Kate Forster leaves the suburban Illinois locale where she completed her residency and takes a job at a busy Chicago hospital. One thing she is reluctant to leave behind is the uniquely beautiful house she's been renting--a spacious and artfully designed refuge with large windows that overlook a placid lake. It's a place in which she felt her true self. It is a winter morning in 2006. On her way to the city, Kate leaves a note in the mailbox for house's next tenant, asking him to forward her mail and noting that the inexplicable painted paw prints he might notice by the front door were there when she moved in. But when the next tenant arrives, he sees a much different picture. Alex Wyler, a talented but frustrated architect working at a nearby construction site, finds the lake house badly neglected: dusty, dirty and overgrown with weeds. And no sign of paw prints anywhere. The house has special meaning for Alex. In a happier time it was built by his estranged father, a renowned architect who allowed his professional acclaim to grow at the expense of his family life. Alex feels a sense of peace here now and commits to restoring the property to its original beauty. He disregards Kate's note until, days later, while painting the weather-beaten jetty he sees a stray dog run across the fresh paint and then towards the entrance of the house, leaving paw prints exactly where she said they'd be. Baffled, Alex writes back, saying that the house had no occupant before him and wondering how she could have known about the dog; while Kate, who just left it a week ago, imagines he is playing some kind of joke on her and fires back a reply. As Kate and Alex continue to correspond through the lake house's mailbox they confirm that they are, incredibly, impossibly, living two years apart, and each at a time in their lives when they are struggling with past disappointments and trying to make a new start. Sharing this unusual bond, they reveal more of themselves to one another with each passing week--their secrets, their doubts and dreams, until they find themselves falling in love. Determined to bridge the distance between them at last and unravel the mystery behind their extraordinary connection, they tempt fate by arranging to meet. But, by trying to join their two separate worlds, they could risk losing each other forever.