Guy Haines is a fictional character from the novel "Strangers on a Train," written by Patricia Highsmith. He is a successful architect who becomes embroiled in a dangerous situation when he meets a stranger on a train. In the story, Guy is drawn into a murder plot after Bruno Antony, the stranger, proposes a twisted idea of exchanging murders to solve their problems. As the plot unfolds, Guy struggles with the moral implications of Bruno's actions and the impact on his life and relationships.