The Mouseheart series does not have a new book coming out soon. The latest book, Return of the Forgotten (Book 3), was published in October 2015.
The first book in the Mouseheart series, Mouseheart, was published in May 2014.
The Mouseheart series primarily falls into the Action Adventure genre. This middle grade series was written for ages 8-12, but can be enjoyed by older readers as well.