According to the internet you're supposed to read this novella between Windwitch and Bloodwitch, so thats what I did. It gives you Ryber's backstory, some insight into the Sightwitch Sisterhood we heard about in the main series and a second timeline in the past. This book consists of diary entries and has some illustrations and letters next to the story. In the beginning I didn't really understand the purpose of this novella other then "this is nice to know but not necessary" because the book startet really slow, but luckily it picked up speed and excitement in the second half. Although I still feel like I don't really know what the things we found out mean and I hope Bloodwitch will give me some clearity on that.