Green Ember Helmer: In the Dragon Tomb, 9781951305376

Green Ember: Helmer in the Dragon Tomb is the twelfth installment in the Green Ember series. Chronologically, it fits after Prince Lander and the Dragon War and before The Green Ember, but the author recommends reading it after The Lost Key. 

In this adventure tale, we learn the backstory of Helmer. We meet him as a young farmer and follow him on his journey to fight back against the darkness.