Mountain of Ashes — John Reed

Matt Thanos is devastated when his wife, Emily, dies in a fiery car wreck. But when an irresistible force hurls him down a wild river into a bizarre labyrinth, his dead wife calls to him from the blackness. She -- or at least her spirit -- is alive. To save her, he must fight his way out of this endless underground chamber, a world ruled by Vaatu, god of the darkness, and cross a time-shifting desert to a crystal city ruled by Raava, god of light. Between these two worlds lies a mysterious mountain made from the ashes of dead souls. Here, the two gods fight for control, a war that has raged for millennium. Since Matt's escape from the labyrinth has disrupted the balance of power, both gods seek to destroy him. The only way to save himself and Emily is to tear the mountain down and destroy their perverted kingdoms.