The Last Secret of Dragons

Mattie and Dinyu have finally turned twelve, they have completed the initiation ceremony and have become true members of the Order of Dragon Riders. Despite the fact that they have already completed several dragon missions, the boys are constantly reminded that they still need to grow up for serious matters. 

But, while watching the preparation for the operation "Sea Depths", they unexpectedly find themselves as the only ones who can attempt to unravel the last secret of dragons