The second entry in Seanan McGuire’s Indexing series does not appear to have any reason to exist. Oh sure, the foreword says something about people asking “What came next” and that this was the answer… but basically nothing is resolved here, a few additional things are now unresolved, and it ends in pretty much the exact same place the first book did. Just skip it until/unless a third entry is ever written.
Speaking of things that should be skipped: Wayward Children.
I know better than to buy something just because I liked some of the creator’s other works. I know better. Worse, I even have a long history of bad experiences with young adult works by authors normally known for writing standard novels. And yet, I still bought the first four of these books and forced myself through them. There are so many negative things I could list about them, ranging from their physical length to their themes to their structure, but ultimately it’s probably best to keep it as succinct as possible and just say “They are young adult novels through and through”.