Responses
That's easy. It's a medieval kind of world with a little magic (since there was a white magician or something who found the butterflies originally in the book) and if she doesn't save Cassis his sister is gonna kill her and her entire family in revenge.
It's like the reader is just thrown in the middle with it with the bare minimum context and a lot of details are missing. What sort of world is this, does it have magic? Why is her survival tied to Cassis? What is she planning to do exactly? These things you have no choice but to keep reading cluelessly until you find the answer.