The Emperor of Nihon-Ja (Ranger's Apprentice Book 10)

Will, you owe it to your friend to find him. Horace is missing. Months have passed since he was sent on a military mission and you, Evanlyn and Alyss set out to discover what has become of your old friend. You find him in Nihon-Ja where the rightful emperor has been overthrown. Now you must face the highly trained Senshi warriors, while Alyss and Evanlyn must overcome their rivalry to seek help from a mysterious group of mountain dwellers.