Last Updated on June 19, 2019, by eNotes Editorial. Word Count: 283
The plot and themes of Strangers on a Train revolve around dualism. Highsmith's thriller questions whether good and evil are really separate entities.
Highsmith's two main characters are complete opposites—the upstanding and conscientious Guy Haines and the evil and indolent Charles Anthony Bruno. However, by drawing them both into a consideration of murder in their first conversation when they meet on a train, the author suggests that they are not as different as they first appear. They both have reasons to consider murder. Bruno wants to kill his father to get his hands on his father's fortune, while Guy wants to kill his wife because she is an adulteress and won't give him a divorce to marry the woman he loves. The reader is sympathetic toward the long-suffering and well-mannered Guy and condemns the crass and ugly Bruno, but, as they both consider murder, Bruno and Guy are not that different.
Over the course of the novel, Guy's life becomes intertwined with Bruno's, to the point where Guy kills Bruno's father after Bruno has killed Guy's estranged wife. They both commit murder, and Highsmith implies that good and evil are not as distinct as they first appear and that even a "good" man can kill. What finally differentiates Guy and Bruno in the end is that Guy is repentant for what he has done, while Bruno is not. Good and evil men can both commit evil. What separates them, in the end, is the fact that Guy has a conscience.
By creating characters who seem like mirror images of each other and by making them commit the same sorts of evil acts, the author artfully suggests that good and evil are intertwined.