I just absolutely love this series!! For me this is actually book 12 but this is the first book in the new part of the series called Cahills VS Vespers. Here is the goodreads description:
The adventure continues. If you are looking for a book that is about adventure, traveling around the world, clues, and yes even murder. These book are like the Amazing Race or the Davinci Code. Now the characters are much older and the books do read that way. I like too how now all the characters who were fighting are now team members learning to work together. These books are pure magic! I thought for sure that after book 10 this series was done, and when I found out there were going to be more books I was disappointed. But once I started reading the new series I was sucked it... need I say it again? MAGIC!