Lynne Reid Banks's _Melusine_ is a fine example of the sort of book I like to call "Teen Celto-Gothic"--defined by mysterious places, dark family secrets, and forces of mythology that make themselves known in the mundane world. Among such novels are older books like Garner's _The Owl Service_ and Pope's _The Perilous Gard_ , and newer books like Liz Berry's _The China Garden_. _Melusine_ is another of this sort, and certainly good enough to be on the shelf with these others.
The story begins as Roger (whose age I estimate at 14 or so), his parents, and his little sisters arrive at the run-down French chateau where they will be spending their vacation. Their first impression of the house is inauspicious; the front rooms are squalid, and the owner, one Monsieur Serpe, a belligerent jerk. But things seem to get better. The part of the house where Roger's family will be staying is well-kept and pretty. And Roger begins to make friends with Serpe's shy daughter, Melusine.
The family vacation turns sinister as Roger begins to hear the sound of something slithering through his room at night. And a struggle he witnesses between Serpe and Melusine suggests a more ordinary but more disturbing horror. Stranger and stranger things happen, and all the while Roger's feelings for Melusine deepen. When he reads about the mythical Melusine in a guidebook, the situation at the chateau begins to become clear--but in order to believe what he knows to be true, Roger must allow himself to believe in the impossible. Can Melusine be saved from the horror at the chateau, or can she save herself? This is a creepy, moody, engrossing novel recommended to those who like that sort of thing. I couldn't put it down.