In the novel's three parts, the third-person narrator generally maintains a consistent tone, which is measured, open, and empathetic. At the same time, the tone goes through slight shifts with each chapter, as the narrator absorbs the thought patterns of the character that focalizes the given chapter.
For example, the first chapter, in which the narrator focuses on Briony's interior monologue, the tone can be described as animated, juvenile, and curious. Although this chapter isn't narrated from Briony's first-person perspective, the third-person narrator has full access to her thoughts and experiences. The animated, juvenile tone gives way to something more jaded and stubborn when the narrator shifts to focusing on Cecilia in the second chapter. Some of the animation remains, however, as Cecilia can't help but take pleasure in the beauty of her surroundings. And the tone remains marked by curiosity, as Cecilia attempts to make sense of her feelings for Robbie—with some resistance. Over the course of the novel, the narrator's tone absorbs elements of the dominant characters' outlooks, while remaining open and measured. Despite having access to their thoughts, the narrator is evidently separate from the characters that direct the chapters.
The transition between the third part and the epilogue involves a shift in narration—which also brings about a shift in tone. Until this point, the novel has been exclusively narrated in the third-person. The epilogue, however, is narrated by Briony in the first-person. Briony's first-person meta-commentary in the epilogue is marked by a contemplative, all-knowing tone. This tone, combined with her claim that she has written the entire story, puts Briony in the position of a kind of higher power.