Lemon in the Basket — Charlotte Armstrong

Everything and everyone is so normal. And then slowly, relentlessly, the evil and the violence begin to take over. To all appearances the wealthy and talented Tylers are a fulfilled, happy family. No one would have guessed the streak of unsuspected madness that lay hidden deep in one of them. Then one day a young prince from the Middle East arrives, seeking medical aid and sanctuary among the Tylers -- and the evil uncoils. Like a growing thing an atmosphere of horror begins to wind itself around the family until it finally explodes in an act of violence that threatens not only the Tylers but the destiny of a whole country.