Arriving in France for a holiday, an English family finds that they are the only guests at the half-derelict chateau belonging to brusque, reclusive M. Serpe. While his younger twin sisters bicker and complain, Roger establishes a tentative friendship with Serpe's daughter, Melusine, an oddly withdrawn girl his own age, learning to help her with the resident goats as each tries haltingly to communicate in the other's language. There is an element of fantasy here--Melusine, in order to escape her abusive father, sometimes becomes a snake--a transformation that parallels a local legend memorialized in a stone carving of a long-ago Melusine who closely resembles Roger's friend. But though the shape-changing provides mystery and suspense, it proves secondary to the present-day events and their dramatic resolution. By introducing the supernatural, Banks is able to treat the issue of incest with delicacy and insight. A few strands are not well integrated here: the snake seems to disappear unexplained, while Melusine's behavior at the end--abandoning her new friends and letting them worry about her as she returns to her ancestral home after her father's death--is not well motivated. But these are small flaws in a story notable for its pungent characterizations, humor, deft use of comprehensible French in the text, and an unusual, compelling plot.