San Francisco Detective Lindsay Boxer is loving her life as a new mother. With an attentive husband, a job she loves, plus best friends who can talk about anything from sex to murder, things couldn't be better. Then the FBI sends Lindsay a photo of a killer from her past, and her happy world is shattered. The picture captures a beautiful woman at a stoplight. But all Lindsay sees is the psychopath behind those seductive eyes: Mackie Morales, the most deranged and dangerous mind the Women's Murder Club has ever encountered. Morales had cheerfully posed as a summer intern with the SFPD while secretly collecting information -- and committing gruesome murders on the side. When Morales disappeared, she was presumed dead and Lindsay thought the nightmare was over. But now Mackie is back and her taste for revenge is stronger than ever.