Even though there were seven middle grade characters and several adults, I was able to keep them all straight, thanks to the differences in their personalities and interests. Brianna is a vlogger who wants to document their experiences, but electronics don't always work well underground, even when she is allowed to have them. Three of the characters have a rather frightening back story about being involved in an earthquake in San Francisco.
The main plot, which I don't want to give away, involves a rather evil plot of world domination with an ecological theme, giving this book one more STEM connection. It's difficult to find books like this, and Slivensky's research is extensive. Science teachers are often asking for recommendations of books with science related topics, and I imagine this will go to the top of many of these lists.