The Faraway Paladin: Volume Three Secundus : The Lord of the Rust Mountains (The Faraway Paladin‪)‬

Will and his new allies at last set out for the Rust Mountains to face the dragon Valacirca. After a nostalgic reunion and an unexpected encounter, the curtain of battle must rise in the lost underground kingdom. What fate awaits the Faraway Paladin? The god of undeath is clear:

"I will say it once more. If you challenge him, you will die."