The Wyrmling Horde Runelords book 7

The monstrous wyrmlings are growing in strength. These creatures have learnt to endow themselves with powers stolen from others, and their capacity for evil is still growing. The people of Mystarria were thrust into the land of the wyrmlings following the merging of two shadow realms, just some among many parallel lands, so now these creatures have millions of victims from which to draw power. The only one who can mend the broken lands - the talented flameweaver Fallion - has fallen into the hands of the wyrmling horde.
Now Fallion's allies must prepare to breach the impenetrable wrymling fortress to rescue him. And unless they can prevent the wyrmlings from gathering more power, these creatures may bring all the shadow worlds under their control. It's not just worlds that are at stake, but eternities.