Dr. Ezekiel Malak, a hospital psychiatrist turned serial killer, is prowling for new victims in Chicago. Bex and the team work to find a method to his madness in a desperate bid to get ahead of him until Malak makes a move no one saw coming.

Arlo Brandt, a hoarder-turned-serial killer, emerges from the Pit with newly found purpose. As Arlo hunts for innocent victims, Bex and the team must get inside a deranged mind.

The student becomes the master when an escaped serial killer from the Pit decides to adopt another inmate's style of killing as a way of paying homage to them.

Bex and the team track the brilliant and beguiling Jenna Wells, the notorious Killer Chemist whose therapy in the Pit has made her even more dangerous and deranged.