One night three years ago, the Tanner sisters disappeared: 15-year-old Cass and 17-year-old Emma. Three years later, Cass returns, without her sister Emma. Her story is one of kidnapping and betrayal, of a mysterious island where the two were held. But to forensic psychiatrist Dr. Abby Winter, something doesn't add up. Looking deep within this dysfunctional family, Dr. Winter uncovers a life where boundaries were violated and a narcissistic parent held sway. And where one sister's return might just be the beginning of the crime.