Taken from the front flap:

Great-Uncle Crom was crusty and solitary, but Clemency insisted on going to stay with him when her parents went off on a concert tour.

It was Crom who showed her the Long Book, the collection of Longbrooke family records. Clemency was fascinated, especially by the sad story of the first members of the family: Christopher and Palatia, sickened and hurt by their father's lack of love and understanding, their father Hector, destroyed by his own meanness--and Hessie, the old village woman, whose dying wish was closely connected with the great house Clemency could see outside her bedroom window on moonlit nights. And when Crom's possession of the Long Book was threatened by a remote cousin, determined to get it by fair means or foul, it was Clemency who sprang to the defence of both Crom and the Long Book--and she also knew it was up to her to do something about the mansion and Hector, trapped in time with it...