Spellbinder by Helen Stringer (Viking).

 
 Belladonna like other members of her family, is able to see ghosts. Often this causes much embarrassment, but after her parents are killed in a car accident, her gift becomes a blessing.  However, when all ghosts, including her parents, start to disappear, Belladonna, her friend, Steve, and even Elsie, a friendly ghost who haunts Belladona's school, set out on a dangerous quest to discover the truth. In the Land of the Dead, they meet a creepy and evil alchemist who's up to no good. Monsters and magical creatures, quirky characters, powerful amulets, and cryptic clues are all a part of this humorous and spine-tingly adventure. Highly recommended (for grades 5-8). The saga continues in the Midnight Gate.