The Fourth Book
Part four will be published at the end of 2017 and is about a new Big Bad called The Lioness who wants to destroy Pala and Mr. Oz. (For those unfamiliar with this TV-trope, the Big Bad is the main bad guy/girl/monster in a TV-series—not to be confused with the monster-of-the-week who is there only for one or two episodes.) The Lioness claims that she wants to free the kidnapped children, but as with everything and everyone in the series, things are not what they seem.
What this book is really about is the role of Iris and her Pantheon of children who have replaced Mr. Oz as rulers of Pala. While they are off on missions and are fighting against mechanical monsters, they also have to deal with a traitor from within and the death of a beloved team member. Iris is also fighting herself: she’s keeping secrets from her team members and slowly becoming the autocratic dictator they so recently dethroned.
The Fifth Book
The last book of the first five (planned for 2018) is about the demise of Pala, the hard choices Iris has to make, and the sacrifices the team must deal with. But it’s also a heist book (think Ocean’s Eleven) where the Superheroes have to recapture Pala from The Lioness (think The Rock). It’s the end of the big story that started with part one and quite possibly the start of a new series.