My Father's Daughter, Paperback/E. L. Konigsburg

Poor Little Rich Boy Winston Carmichael has it all: a big house, servants, vacations in Palm Beach, and a fancy private school. But with overprotective parents and a sense of responsibility for his younger sister, Heidi, Winston sometimes feels more as if he's living in a prison than a dream. Then one day a woman appears at the front door claiming to be Caroline -- Winston's half sister, who was kidnapped and presumed dead long before he and Heidi were born. Is she really Caroline? Is she an imposter? Or is she something far more complicated than either? And does she hold the key that could unlock the door to Winston's prison?