A series of shootings exposes San Francisco to a methodical yet unpredictable killer, and a reluctant woman decides to put her trust in Lindsay Boxer. The confidential informant's tip leads Lindsay to disturbing conclusions, including that something has gone horribly wrong inside the police department itself.

The hunt for the killer lures Lindsay out of her jurisdiction, and gets inside her in dangerous ways. Lindsay's friends and confidantes in the Women's Murder Club warn her against taking the crimes too much to heart. But with lives at stake, the detective can't stop herself from following the case into ever more terrifying terrain.

A decorated officer, loving wife, devoted mother and loyal friend, Lindsay is confronting a killer who is determined to undermine it all.