Dr. Olivia Simon is on duty in the emergency room of North Carolina's Outer Banks Hospital when a gunshot victim is brought in. Midway through the desperate effort to save the young woman's life, Olivia realizes who she is—Annie O'Neill. The woman Olivia's husband, Paul, is in love with.

When Annie dies on the operating table, she leaves behind three other victims. Alec O'Neill, who thought he had the perfect marriage. Paul, whose fixation on Annie is unshakable. And Olivia, who is desperate to understand the woman who destroyed her marriage.

Now they are left with unanswered questions about who Annie really was. And about the secrets she kept hidden so well.