Secret Window

After catching his wife Amy having an affair with their friend Ted, mystery writer Mort Rainey retreats to his cabin at Tashmore Lake in upstate New York, while Amy stays in their marital home. Six months later, Mort, depressed and suffering from writer's block, has delayed finalizing the divorce. One day, a drawling Mississippian caricature named John Shooter arrives at the cabin and accuses Mort of plagiarizing his short story, "Sowing Season". Upon reading Shooter's manuscript, Mort discovers it is virtually identical to his own story, "Secret Window", except for the ending.