I like this book, the sequel to Black and White, too… just not as much.
The focus of this book is much less on Jet and Iridium. The book still alternates between current action and flashbacks, but the flashbacks are not to young Jet and Iridium, but to their parents–and not just their parents, but the whole alpha-team of their parent’s day. It’s a good change for getting more world building and explanations into the story, but gives up the strong focus on Jet and Iridium that made the first book such a pleasure.
So the crisis Iridium triggered at the end of Black and White is the heart of “now”; dealing with it is exhausting, but Jet and Iridium grow and step into new leadership roles. It’s a fine “adulthood and accepting the burdens of responsibility” story, but it’s much shorter than the previous book. The alternate era story is interesting and good worldbuilding–it’s nice context for both books–but no character gets enough time to make them truly sing. (Luster is much better formed by the end of the flashbacks; his final “then” scene with Night does a great job of defining them both.)
I think this book was the end of their partnership in exploring this world. If they resumed, the story going forward would be significantly different due to Jet and Iridium’s new relationship and roles. Done well, I’d enjoy more stories.