Beyond the Grave: 05/17/13
Beyond the Grave by Jude Watson is the 4th of the original 39 Clues series. It takes the Cahill siblings to Egypt — first to Cairo and then along the Nile to historical points of interest.
Book four breaks with the format of having two countries to visit, to focus more generally on both the history of ancient Egypt as well as the development of Egyptology starting with Napoleon's explorations into Egypt.
As Amy and Dan learn about Egypt, they get a glimpse into the life and times of their grandmother. Although most of the other families aren't in this book, there are still some hair-raising scenes, including one in a submarine.