Spear of Heaven
by Judith Tarr
Worldgates are a great magic and a great convenience: opening the way from one world to the next, and from one side of a world to the other. Now the mages of the Gates are exploring a new continent and forging new alliances, led by the Master of the Mageguild and the heir to the throne of Sun and Lion. Suddenly, the Gates begin to fall... and the Master and the royal heir are trapped in a hidden kingdom on the far side of the world, with no way out but through the broken Gates.