'Jumping Jack!' someone at the front of the class hissed and the rest of the class began to murmur, 'Jumping Jack, jumping Jack...'
Jack doesn't like the look of his new school one bit. It's so old and spooky-looking that Jack is convinced that it is haunted, and all the children in his class seem cold and unfriendly. Except one. A lively, mischievous girl in strange, old-fashioned clothes, who tells him her name is Jenny.
But there is a mystery surrounding Jenny. For one thing, nobody else seems able to see her! Could she possibly be a ghost? All Jack knows is that she is his friend and he is glad that she is there, helping him through the first awkward days. But it is only when one of his classmates is in desperate danger that Jack is to finally learn the real truth about Jenny...