While investigating a series of fires that were set on a college campus in Tempe, Arizona, the BAU must think outside the box in order to identify the unsub. Meanwhile, Gideon continues to recover from a near-death experience.
This episode provides examples of:
- Alone with the Psycho: The episode continues where the previous one ended, with Gideon being held at gunpoint by the Footpath Killer.
- Attack Its Weak Point: Gideon irritates the Footpath Killer by telling him he's a dumb bedwetter according to the profile. The Killer tries to order Gideon to take the camera to take his pre-mortem photo as per his ritual, but Gideon has made him so angry and nervous he can't pronounce the word, so Gideon makes him even more mad by smiling and claiming he doesn't understand what he says. Eventually, the Killer becomes agitated enough for Gideon to disarm him successfully.
- Creepy Souvenir: The Footpath Killer leads Gideon to a closed room with post-mortem photos of some of his victims (all shot on the forehead), in contrast to the ones outside that were taken when they were still alive.
- Rule of Three: The arsonist is obsessed with the number three.
- Super OCD: The killer has OCD relating to the number three. They tend to repeat words and actions three times and is compelled to kill with fire whenever she encounters a trinity of threes. When confronted they admit what they are doing isn't right, but as Hotch explains the unsub isn't killing because they want to, but because they are compelled to.