The Gate of Gods - Martha Wells

Tremaine Valiarde and a small, brave band of heroes ventured into a wondrous new realm on their desperate mission to save Ile-Rien from the conquering Gardier. Now, as a relentless enemy creates chaos and destruction -- with the fate of the magical city of Lodun hanging in the balance -- the last hope of a land besieged may rest on the far side of a secret portal.

But the doorway leads to a mysterious ruin hidden behind the awesome Gate of Gods -- and to perils that dwarf anything Tremaine and her allies could have possibly imagined. . . .