A Charge of Valor (The Sorcerer's Ring #6) by Morgan Rice

In A CHARGE OF VALOR Thor continues on his quest, deeper into the Empire, to retrieve the stolen Destiny Sword and save the Ring. As he and his friends meet unexpected tragedy and lose a member of their close-knit group, Thor and his remaining friends become closer than they ever were, learning that they must face and overcome adversity together. Their journey takes them to new and exotic terrains, including the desolate Salt Fields, the Great Tunnel, and the Mountains of Fire, as they face a host of unexpected monsters at every turn.