The second episode of Criminal Minds , titled "," follows the Behavioral Analysis Unit (BAU) as they hunt an unconventional serial arsonist on a college campus in Tempe, Arizona. Unlike typical arsonists who watch their fires for pleasure, this "unsub" (unknown subject) kills victims in private, suggesting a different psychological driver. The Arsonist's Profile

The unsub is obsessed with the number three, believing it has divine significance.

The team struggles because the perpetrator doesn't fit the standard profile of a male arsonist motivated by power or revenge. Dr. Spencer Reid eventually identifies the motive as —a form of Obsessive-Compulsive Disorder (OCD) involving religious or moral obsession.

Agent Hotchner confronts Clara, attempting to talk her down to buy time. When she refuses to stop, Hotchner shoots her in the leg, allowing the team to save the students. Criminal Minds Season 1 Episode 2: "Compulsion" summary

Fires are set in patterns of three (e.g., the first on March 3rd at 3:00 PM), and the unsub performs ritualistic actions in threes, such as turning doorknobs or repeating words.

Clara traps three classmates in a science building elevator on the third floor, dousing them with chemicals and preparing to set them ablaze.