A Joust of Knights (Book #16 in the Sorcerer's Ring)

In A JOUST OF KNIGHTS, Thorgrin and his brothers follow Guwayne's trail at sea, pursuing him to the Isle of Light. But as they reach the ravaged isle and the dying Ragon, all may be just too late.
Darius finds himself brought to the Empire capital, and to the greatest arena of them all. He is trained by a mysterious man who is determined to forge him into a warrior, and to help him survive the impossible.
But the capital arena is unlike anything Darius has seen, and its formidable foes may be too intense for even he to conquer.
Gwendolyn is pulled into the heart of the family dynamics of the royal court of the Ridge, as the King and Queen beg her for a favor. On a quest to unearth secrets that can change the very future of the Ridge and save Thorgrin and Guwayne, Gwen is shocked by what she discovers as she digs too deep.
Erec and Alistair's bonds deepen as they sail further upriver, into the heart of the Empire, determined to find Volusia and save Gwendolyn—while Godfrey and his crew wreak havoc within Volusia, determined to avenge their friends.