The tone of this novel is, for the most part, heartfelt and candid. Louisa shares her feelings quite openly with the reader, and it is, after all, a love story, so there are plenty of feelings to go around. This candidly emotional tone is a reflection of a candidly emotional narrator, and on the occasions when the narrator switches, the tone tends to also. Therefore it becomes matter-of-fact and restrained when Nathan narrates, or cold and clinical when narrated by a government bureaucrat. Even when narrated by Lou in its more heartfelt tone, though, the novel avoids sentimentality, thanks partly to joke-heavy dialogue.
The mood is more variable, and tends to swing between hopeful anticipation and dread, following the novel's plot structure. When the protagonist is hopeful, the narration is rich with lovingly described images, and layered with figurative language, creating a relaxed, luxurious mood. When the protagonist feels dread, though, this is reflected in the mood as well, since the images become fewer and more unpleasant, the sentences shorter, and the language more literal. This more utilitarian prose discourages relaxation and prompts readers to feel anxious.