Elias wasn't normally the type of brother to keep secrets. When he was seven, he had found her birthday money lodged between the trash bag and the side of the trash can. He was smart, and Ruby knew he could have lied about it, but he was also kind. He gave her the money after dinner later that night. Last year as he started to realize he liked girls, he and his first "girlfriend" went around telling everyone how they were practicing kissing. His girlfriend fancied herself a ten-year-old trends setter, and he was none too shy about helping start a trend around public grade school relationship tracking. So when he started spending the first couple of hours after school every day locked in his room, Ruby knew something was amiss.

Some myster, it can be falsely resolved to the reader in the first chapter but then come back into the story later after some other minor conflict(s). The main point of the first book is to introduce the characters and the main plot concept, but the main plot concept doesn't really need to be important in the first book, just the characters and the small differences about the world and how that affects a typical ten- and twelve-year old as they go about their normal life. Then subsequent books can reveal more about the larger plot(s) surrounding the window between worlds. Fiction is hard.