Stormriders, by Roxanne Longstreet Conrad
(writing as Roxanne Longstreet)

Lightning rips through their house, and Brion and his family are swept into a violent Essence Flow Storm, into the dangerous, spellbinding world of Kulthea -- the Shadow World. Brion's son is now missing, and he will do anything in this strange world to get him back. But there is one person who will stand in his way. His wife, Kella.

She is treacherous. Even murderous. And in the magical realm of Kulthea, so much more is possible. A darkly powerful sorcerer has awakened new and terrifying hungers within her. And the search for their son will plunge them all into a battle between the servants of Light and the minions of Unlife. A battle for their very souls ...