Grace Sachs, a happily married therapist with a young son, thinks she knows everything about women, men, and marriage. She is about to publish a book called 'You Should Have Known', based on her pet theory: women don't value their intuition about what men are really like, leading to serious trouble later on. But how well does Grace know her own husband? She is about to find out, and in the place of what she thought she knew, there will be a violent death, a missing husband, and a chain of terrible revelations.
Grace Sachs er en succesfuld psykolog og gift med en læge. Hun har skrevet en selvhjælpsbog om, hvordan kvinder ikke følger deres intuition, når de vælger partnere, og derfor er nemme ofre. Men så bliver en kvinde myrdet og Graces egen mand forsvinder sporløst.