The other daughter - Lisa Gardner

A nine-year-old girl is abandoned, unconscious in a hospital ER. When she comes round, she remembers nothing about herself or her past. The girl is adopted and raised as Melanie by Dr Harper Stokes and his wife, whose own daughter Meagan was tragically murdered.

Twenty years later, a reporter starts investigating Melanie's true parentage and an FBI agent becomes involved in the tangled mystery of her past. And when grotesque messages and gifts start arriving, Melanie begins to fear that the family she loves the most may be the very people she should trust the least...