Sheila, young international leader of haute couture, is found murdered in her Park Avenue penthouse. Two floors down, the distinguished middle-aged millionaire-Ashton McKell-is hauled off to jail. Next to go, Lutecia, his shy patrician wife. And then-Dane, their handsome, sensitive son. Together, a triangle of murder suspects. Ellery, immobilized, can trick the police into becoming his 'legmen' if he discovers The Fourth Side of the Triangle.