Dragon's Pearl — Jane Toombs

Centuries ago, Merlin stole forbidden magic from the immortal black dragon to try to save King Arthur. To prevent the dragon from exterminating mankind in retaliation, Merlin set wards that forced the dragon into the depths of a mountain cave in Wales. But wards fail with time. To prevent the dragon from escaping, one of Merlin's blood and another of dragon's blood, plus a third, must reset the wards as they weaken. When the last of Merlin's blood and the last of dragon's blood left Wales for America, the evil within the dragon came, too. He is now tethered in the depths of an abandoned copper mine in Michigan's Upper Peninsula. But the wards are failing and those who must reset them aren't aware of their duty. If this evil isn't contained chaos will be let loose. And time is running out…