Letters are a plot device that reveals information to the characters in ways that spur the story along. The letter that Mr. Hawkins writes to Ferdinando, which Caleb finds, proves Mr. Hawkins’s innocence of murdering Barnabas. that the same letter creates Caleb’s need to further investigate Ferdinando by sparking his curiosity.

Letters appear again when Caleb writes one during his attempt to leave the service of Ferdinando; this heightens the tension between the two men and leads Caleb to realize just how bad the consequences of his actions will be. Mr. Forester also writes a letter to Caleb to persuade the latter man to return to town to defend his case. When Caleb receives the letter from Laura telling him to stay away from her, it helps push him over the edge into seeking vengeance against Ferdinando.

The wanted ads, while not letters, similarly work to move the plot along and create conflict between the characters. The wanted ad that describes the Irish robbery is the reason that Caleb never makes it out of England. An ad also is what makes Gines Caleb’s archnemesis because it happens to pass through his office at the right time.