Spoiler warning! This article contains plot details about a newly released or upcoming book.
Unstopable is the the series that will follow the final book of the Cahill vs. Vesper series. It's first book will be out in October of 2013, and is written by Jude Watson. There will be four books in the series, and they will be about Amy and Dan exploring lost civilations. Reportedly, Jude Watson has been researching Illiad and Troy, and she has said that part of the first book will be in Turkey. That is the only information we have on this series at the moment. To learn more, and for an interview with Jude Watson, go to this link -- Unstoppable