The Keeper — A.J. Smith

Jelly Jones' summer has gone from boring to miserable. First, her best friend leaves her for summer camp--all summer--then her uncle disappears! When the rest of her family goes to help search for the missing uncle, she is shunted off to stay with the stern old lady across the street. While Jelly is at the depths of her despair, a whisper in the dead of night leads her to a book in the forbidden attic ... and the adventure of a lifetime.