The Mysterious Four series does not have a new book coming out soon. The latest book, Monsters and Mischief (Book 3), was published in September 2011.
The first book in The Mysterious Four series, Hauntings and Heists, was published in May 2011.
The Mysterious Four series primarily falls into the Mystery genre. This middle grade series was written for ages 8-12, but can be enjoyed by older readers as well.