Sandy Kinsolving is on a flight from London to New York, not knowing what awaits him.  His father-in-law, also his boss, has had a massive stroke, and Sandy has no way of knowing if the old man's promises of a pertnership in the family business have made it into his will.  He does know that his wife, Joan, has anything to say about it, he'll be out on the street. 
 
At this vulnerable moment in his life he strikes up a conversatoin with the friendly stranger sitting next to him.  They have a drink and watch the movie, which turns out to be Alfred Hitchcock's Strangers on a Train.  After the fil has endded, and after a few too many drinks, the two men discover that they both have wives who are making their lives difficult, and they decide to see if they can iron som wrinkles out of the film's plot.
 
By the time Sandy Kinsolving's plane has landed in NY, his life has changed irrevocably, although he does not yet know it.  Awaiting him are wealth, security, and the freedom to purse his lifelong ambitions.  But lurking in the shadows of his life are a brutal murder he cannot bring himself to prevent and a madman who stalks his every waking moment.