The Changeling — Philippa Carr

SHE KNEW GREAT HAPPINESS UNTIL THE DAY HE ENTERED HER LIFE...

She was young Rebecca Mandeville, a girl fatherless since birth, a sprite who was equally at home on the Cornish moors and in Victorian London. But when her mother married the roguish Benedict Lansdon, her world turned bleak. Soon Rebecca was motherless as well, left with her hated stepfather and her new infant sister, Belinda -- a hellion determined to get her way at all costs...

But young girls grow up and Rebecca was no exception. A clever beauty, she had learned to accept life's pain -- until family tensions erupted in one catastrophe after another, until Benedict's beautiful new wife disappeared amidst cries of murder, until only Rebecca could save the man she had once despised...