"Conor O'Toole has never in his life been in a place as casually glamorous as this New England community, a gated world its residents fondly call "The Neck." He's taken a summer job here as a tennis instructor, living in a guest cottage in exchange for lessons and a chance to study for the bar exam, far away from the stress of the tiny Yonkers apartment he usually shares with his diabetic mother. But, grateful as he is for the blissful beauty of the...