Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
The tone of The True Confessions of Charlotte Doyle is complex, to be sure. While we're always getting Charlotte's most private and intimate thoughts, the way in which those thoughts are delivered varies. Charlotte's writing is sometimes demure and unsure, but it can also be confrontational and angry. Her tone is variable and changes through the novel as she develops, which makes sense. For example, the older, adult Charlotte who introduces the novel is pretty aggressive. She writes:
If strong ideas and action offend you read no more. Find another companion to share your idle hours. I intend to tell the truth as I lived it. (Preface.1)
Compare this attitude with young Charlotte's:
Once alone I again gave way to hot tears. Not only did I feel completely isolated, but something worse: I was certain that all the terrible events of the day – the death of two men! – had been caused by me! (12.63)
Pretty different, right? One voice is sure of herself and a smidge angry; the other is crying, confused, and oh-so pitiful. Notice, too, how personal and confessional Charlotte's thoughts are.