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.

Bex and the team race to catch Mark Marsden, known as the Widower, a handsome and charming serial killer who murdered three of his wives in cold blood. Everything changes when Mark decides to take a new bride.

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 hunt their most depraved serial killer yet, Tom Beecher, who seeks pleasure in other people's pain.

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.