Dr. Olivia Simon is on duty in the emergency room when a gunshot victim is brought in. Soon, Olivia realizes who she is: Annie O'Neill, the woman Olivia's husband, Paul, is in love with. When Annie dies, she leaves behind three other victims: Alec O'Neill, who thought he had the perfect marriage; Paul, with his unshakable fixation; and Olivia, who needs to understand the woman who ruined her marriage. Now they are left with unanswered questions about Annie and about the secrets she kept hidden.