The winters in Maine are long and lonely. That's why it seems the perfect place for Karen to escape her golden cage in Boston. She moves into a secluded wooden cottage by the sea to write a book.
There loneliness and diffuse doubts cause Karen to lose control of her novel. The events and characters of the story come alive. Karen feels observed and starts to hear voices. And there is that inexplicable knocking sound. Her fears invade her dreams. Suspense turns into a nightmare. Her story and her characters become more and more entangled with her own reality. Is the danger she perceives real or just a figment of her imagination?
But then a very real crime occurs.