Legacy of the Darksword (The Darksword #4)

Twenty years ago, the magical land of Thimhallan was destroyed with the forging of the Darksword, leaving a small group of survivors exiled on Earth.  Only Joram, who created the Darksword, remained behind in the shattered land. But another catastrophe beckons, as an alien race plans to annihilate the remaining colonists. But Joram has forged another Darksword, and Earth's leaders see it as their only salvation. And it is up to Saryon, an old friend of Joram's, to put the sword in safe hands and possibly save the planet.