Storm Warning.
The ninth clue is Mace
Storm warning
The title is Storm Warning
There is not going to be a 12th 39 Clues book, but there is going to be a new 39 Clues series. The first book in the new series is called The Medusa Plot by Gordon Korman.
Into The Gauntlet
It is called the Emperors Code
It is called The Black Circle.
Beyond The Grave.
Vespers Rising.
Storm Warning
It's called The Emperor's Code
The name of the 10th 39 clues book is Into The Gauntlet.