V.M. Sang 
The Never-Dying Man [EPUB ebook] 

After finding Sauvern’s Sword, the companions set off to help a friend rescue his child from kidnappers. Instead, they stray into Erian and find preparations for war. They are drafted into the Erian army but are recognized by an old enemy, who arrests some of them and takes them to Frelli, the capital of Erian, where they are put in jail.
The Master of Erian frees them and offers them work. Meanwhile, Carthinal has to face some unpleasant truths about himself. Is his desire to further his magical career more important than his friends and country? After they discover terrible truths about the Master and his magical research, they will need to escape in order to tell the leaders of Grosmer about the plans for war.