The other daughter - Lisa Gardner

In Huntsville, Texas, a man goes to the electric chair for the kidnap, torture and murder of six small children. In Boston, Massachusetts, a nine-year-old girl has been admitted to ER, unconscious and full of morphine. When she comes round, she remembers nothing about herself or her past.
This girl ? twenty years later ? is the heroine of THE OTHER DAUGHTER. Melanie Stokes has been adopted and raised by Dr Harper Stokes and his wife, following the tragic murder of their four-year-old daughter, Meagan. Now someone is targeting the family, sending grotesque signals and messages, suggesting that it is they, not the executed serial killer, who may have been responsible for Meagan?s death. In an even more horrible twist, a journalist approaches Melanie and tells her that her birth father was the executed murderer.
David Riggs, Special Agent, sent in under cover to investigate a medical scam in which Dr Stokes is implicated, becomes romantically involved with Melanie, and then with the whole tangled mystery of her past.