Banks (The Mystery of the Cupboard, 1993, etc.) introduces readers to twin girls--one purely good, one purely evil--who make a hash of their well-intentioned parents' lives. From birth, Angela is the embodiment of goodness; people blissfully melt at the sight of her. Everyone loathes nasty, screaming, purple-faced Diabola: Her parents have to pay a pair of street bums to be her godparents, and the vicar is so startled by her mean little eyes that he drops her in the baptismal font. Diabola, absolutely without conscience, grows up and goes on wreaking havoc, culminating with the burning down of the school. She's by far the more engrossing character, but sweet, passive Angela has more to her than meets the eye--she's the only person on earth with a modicum of control over Diabola. Banks gives her story a contemporary setting and tries to make the twins' parents as normal as possible, but the conceit of the piece--good and evil personified-demands fairy-tale language and magical (perhaps spiritual) intervention. The two approaches don't always blend: Banks often sacrifices subtlety for the broad satire of Roald Dahl's work, but the conclusion is both satisfying and novel.