The Scarlet Letter is the best known and most read novel by Nathaniel Hawthorne. Set in Puritan New England in the 1600s, Hawthorne is largely addressing the theme of the individual versus society. Hawthorne is writing the novel in the 1800s, during the Romantic period. This time period shows a shift in focus within culture, moving from a communal mindset to a more individualized focus. Hawthorne's uplifting of the individual is captured in his tale's moral, "Be true, be true, be true." Hester becomes a romanticized hero because of her faithfulness to herself over the regulations of an oppressive and judgmental society. In this sense, she is contrasted with Dimmesdale, who sacrificed his individuality for the sake of society's acceptance.
Themes of Guilt vs. Innocence and Sin's Consequences are also seen in the novel. Hawthorne is at times ambiguous about his definitions of "sin" and "guilt," however. The novel seems to explore different levels of sin, showing different consequences accordingly. Hester wears her consequence with pride, and, remaining true to herself until the end, is able to change the people's opinion of herself and her sin. Dimmesdale hides his sin, and his consequences therefore are also hidden until the end. However, his sin is not just against society's rules. He also sin by denying himself for the sake of society. His consequence is more severe -- a growing weakness that ends in his death. Chillingworth's sin is against others -- a sin aimed at causing pain. Like Dimmesdale, his sin is secret and the consequences are slow and hidden, concluding in his own death as well.
Several conflicts are developed in the novel to demonstrate these themes. Hester versus the townspeople (or society) is a main, external conflict. We also see internal conflict within both Hester and Dimmesdale, and they wrestle within themselves to be individuals. Another major external conflict is Dimmesdale versus Chillingworth, as Chillingworth tries to enact revenge on Dimmesdale. All of the main conflicts are resolved in the final scene -- Hester and Dimmesdale are able to reveal their true selves to the town, Dimmesdale is able to escape Chillingworth once and for all, and Hester is finally able to move on from her past.
There are some minor conflicts as well. Hester and Pearl have to fight early in the novel to stay together. Hester and Pearl also have conflict with each other, as Pearl is both her mother's blessing and curse. Arguably, Chillingworth is in a losing battle with himself as he pursues revenge. Hester and Chillingworth also have conflict with each other, due to her affair and then her promise to keep his identity a secret.
The Scarlet Letter does seem to have two distinct plots. The plot following Hester and her conflicts would be the main plot. We consider this the main plot for several reasons: Hester is the character most focused on, Hester is the character wearing the scarlet letter, and Hester is the character seen in the first and last scenes of the novel. The subplot would be Dimmesdale's conflicts. He has a secret scarlet letter, he is also experiencing conflict in connection with his sin, and he is also seen in the final scene. These two plots intertwine throughout the novel, though both have distinct rising action, climax, and resolution.