A female serial killer is on the loose, and it's up to FBI agents Dillon Savich and Lacey Sherlock to track her down - and stop her before it's too late. There's evidence that the woman, Kirsten Bolger, has a killer bloodline, too: a connection to the notorious Ted Bundy only complicates the case. But the crack team of Savich and Sherlock are on it - and better than ever.

At the same time, Special Agent Lucy Carlisle learns from her dying father that her grandfather hadn't simply walked away from his family twenty-two years earlier: he had, in fact, been murdered by his wife, Lucy's grandmother. Determined to uncover the truth, Lucy moves into her grandmother's Maryland mansion, where she finds a skeleton in a steamer trunk and an old ring sewn inside the body's trouser cuff. She's led to her grandfather's secret papers, and learns about her grandmother's obsession with the ring and a mysterious group called The Protectors.

As the hunt for Bolger escalates, Savich and Sherlock find themselves in her crosshairs. It's up to Lucy to stop this deranged woman and save Savich and Sherlock before it's too late.