The Thirteenth Unicorn
by W. D. Newman
Ben Alderman and his sister Casey discover a portal to a world of magic, a world discovered, shaped, and settled by wizards. It is a world where elves and dwarves are locked in mortal combat against a witch who is trying to free the last wizard from exile. The witch has been defeated once before but with the combined power of the wizard, no one will be able to stand against them.