Where Are You Now? - Mary Higgins Clark

How far would you go to keep a secret?

It has been ten years since 21-year-old Mack went missing. A Columbia University senior, he walked out of his room and has not been seen since. Every year he calls his mother on her birthday, on his birthday, and on Mother's Day. He assures her he is fine, refuses to answer her frenzied questions, then hangs up. Even the death of his father on 9/11 does not bring him home.

Mack's sister, Caroline, has now endured two family tragedies. Determined to solve the mystery surrounding her brother's disappearance, she sets out to discover the truth. But with it comes a secret that someone will do anything to protect, leading her to a deadly confrontation with an unexpected enemy…