The Ring Bearer (Book 6 of The Warden) - The Warden, #6

The warden's prison is on the cusp of major changes. Be it the mounting evidence that the elementals are not who they appear to be, the reckless actions of his employees, or the political coop happening right inside his walls. When one of the prison's long time tenants finds the key to his military objectives, he will do anything to get what he wants. And he isn't the only one. The elementals are just as intrigued by the new powers emerging in one of the warden's employees.
Caught between the power-hungry and the desperate is not a good place to be.