Bad Blood by John Carreyrou

When Cassie Hobbes joined the FBI’s Naturals program, her main mission was to uncover the truth about her mother’s murder. But everything she thought she knew has been turned upside down. Her mother is alive, and the people holding her are part of a powerful, secretive group far more dangerous than anything Cassie and her team have ever encountered.

As the Naturals dig into the deadly secrets of this shadowy organization—one that has been quietly orchestrating murders for generations—they find themselves in a desperate race against time. 

With a growing body count and the danger striking closer to their own lives, it becomes clear that this time, the Naturals aren’t just hunting serial killers—they’re up against something far bigger and far more deadly.