The Cry Beyond the Door by M.A. Koontz

After being kidnapped and almost killed by a psychopath, Darla "Dar" Kelly's only hope was for a normal life. But when she stumbles across evidence that her recently murdered father had hired a PI – and had kept it from her – her life becomes anything but normal. Suspicious that someone is trying to block her every attempt to solve the mystery, Dar's problems mount further when a bizarre recurring dream and a targeted John Doe, lead to deadly complications that once again plunge her life into danger.