New fiction: 'The Water's Lovely.'

When it comes to people – ruthless and otherwise – few writers can match wits with Ruth Rendell. With "The Water's Lovely," her 63rd novel, Rendell eschews whodunit for whydunit and, along the way, delves into some of life's most mysterious wonders: revenge, guilt, slights, and, most delicious, class warfare. The story centers on two sisters, fashionable Ismay and dowdy Heather, who share a murderous secret. A decade earlier, the sisters' stepfather was found dead in the bathtub. On that day, Heather emerged at the top of the stairs with her clothes soaking wet. The daughters and their mother told police the drowning was an accident and no one has discussed it since. Now in their 20s, the sisters live together in a flat below their mentally ravaged mother. As they become enmeshed in serious romantic relationships, the fallout from their dark secret wreaks havoc. Rendell makes superb use of the family's orbit of friends and acquaintances: a small-time conniver who caters to the elderly, a 30-something male nurse who still lives with his insufferable hypochondriac mother, and the ruthless playboy Ismay adores in spite of her better judgment. As for judgment, Rendell provides a head-spinning finale that satisfies even as the dread of its symmetry dawns on the reader. This is a master at the height of her powers. So what are you waiting for? Dive in. Grade: A