Emma in the Night

Emma in the Night by Wendy Walker can be described as "intelligent suspense". There is a lot of psychoanalysis of the characters, and it adds to the plot rather than slow it down. I ended up liking even the not-so-likeable protagonists, and I was sorry when I ran out of pages to read.

Blurb:
One night three years ago, the Tanner sisters disappeared: fifteen-year-old Cass and seventeen-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.