I've been thinking quite a lot of about Norra, oddly enough. Whenever I find something intriguing, I try and find as much evidence as I can. Im here making this post in order to present that evidence to you. We know that Norra is the yordle master of Yuumi and that Norra used Book to travel to different places in order to collect random artifacts. We also know that Yordle's seem to be quite curious spirits/beings. So with that in mind I think that Norra is on the Shadow Isles, let me explain how I got to that conclusion.
Norra went to a place that is dark and quite dangerous so she ripped not one but many pages from Book, she didn't want anyone to follow her to that place as even Book stayed and didn't follow her. The only places that seem really dark to us is the Void (portal in Icathia) and the Black Mist. Now since Norra tore out the pages she traveled to, Yuumi can't follow her directly there and that is why Norra is **not** in the Void/Icathia. Keep that in mind.
>She saw the book on her master’s desk and flipped through its pages in a panic, noticing that** some were torn out entirely**
As we all noticed by now, some in- game items are lore related. For example: Frost Queen's Claim, Seeker's Armguard, Guardian's Orb and many others I can't think of right now. If Im thinking this out correctly, **Lost Chapter** was never lore- relevant until now. If you look at it in detail, you will notice that the page has a symbol on it, it's the Shadow Isles symbol. Now I wouldn't have made this post if Yuumi's bio didn't mention multiple pages, and it does! The image shows that the pages were not taken out with a gentle hand. They were torn out. If you rewatch the yuumi [teaser](https://www.youtube.com/watch?v=a0nz9hde9q0) you will notice that Book uses simple symbols for factions and places. The book isn't written in a complicated way, it's very straightforward. This leads me to believe that the **Lost Chapter**, in its simple writing, is the page(s) that was torn out of Book since there is literally a lost chapter...
Now the only question left is why? What would Norra want in the Shadow Isles? I know she is curious as most yordles are but she isn't stupid to risk her life just to discover a few artifacts there. She even left Book because she knew how dangerous it is there and how dangerous it would be if someone from the Shadow Isles got Book. In my opinion she is on a very risky mission to do something, not sure what tho.