Dan and Amy decided to take a break from the Cahills after nearly dying from combating Pierce and his thugs.
When this coup is realized, Ian Kabra and Cara Pierce are expelled from the Cahill home in Attleboro, Massachusetts.
The leader of the coup is the Outcast, and he plans to replicate history's worst disasters in order to test Cahill leadership.
The cover is green, with the yellow oval saying "The 39 Clues" It also features the skyline of a modern city, most likely Rotterdam, Netherlands, a large port.
The note at the end of the book reads: " My fellow ‘lost’ dragons: The science is sound.
The book begins with Alek Spasky in the depths of the North Sea, with a captain of sailors that salvaged sunken vessels.
Spasky is searching for the Kraken, a Russian submarine that had burned up and sunk into the North Sea.
During the Cold War, many submarines and airplanes had crashed into the ocean, with intact nuclear bombs known as broken arrows.
Meanwhile, on Mount Fuiji, Japan, Sammy and Nellie order grilled cheese sandwiches to go.
Katrina wreaked profound devastation, The same fate awaits a new coastal nation… The Gateway floods when autonomy fails, The torrent erases the Dutch king’s trail.
In Attleboro, Massachusetts, the Outcast tells Mr. Berman to get rid of Saladin, the family cat.
Dan also learns about broken arrows, and theorizes that the Outcast will detonate one to create a tsunami.
Meanwhile, back in Boston, Beatrice insults everyone in her will, and leaves everything to the Porcelain Cats are People Too Foundation.
Meanwhile, on Mount Fuji, Nellie and Sammy encounter Magnus Hansen, the current Tomas leader.
In the black files, Ham discovers that Grace purposely got his father expelled to prevent him from being Tomas leader.
On Mount Fuji, a blizzard hinders Sammy and Nellie, and they camp out in a small snow cave.
All of the ships safely come inside the dam except for a small fishing boat with engine problems.