What is the theme in Mind Prey by John Sandford?

Mental Illness is a major theme in the book. Andi Manette is a psychiatrist. Andi sees many patients on a daily basis, specializing in criminal behavior, such as child molestation. When Andi is kidnapped along with her two young daughters, police immediately begin to focus on her patients. In Andi's files at her practice police find several cases in which Andi mentions patients attempting to flirt or make passes at her and still others in which Andi failed to report an active child molester. However, the police cannot find a patient whom they can believe is the man behind the kidnapping.