When Reyes uses numerology to connect the murders of several women, she and Scully become trapped with a mysterious checker-playing man who may or may not be the killer.
In a casino, Mad Wayne loses at cards and heads to the bar to converse with Mr Burt, who is playing solitaire. Wayne's attention turns to a woman, who he follows to the bathroom. A short time later, the woman is found dead.
At the FBI, Reyes asks Scully if she believes in the hypothesis that the universe is knowable as a simple mathematical equation. Scully doesn't, and is disbelieving when Reyes attempts to tie together several murders by using a mathematical calculation. Scully notices a pattern in the bruising of the victims' skin, speculating that it was caused by a ring the killer wears.
Meanwhile, Mad Wayne returns to the rundown hotel where he lives, and notices Mr Burt playing three-card Monte in the street below. Wayne confronts Burt and warns him to stay away.
Reyes enters Wayne's building to consult a numerologist, Vicki Burdick. Burdick doesn't really believe in numerology, however, but reluctantly promises to run a complete numerology in the hope of producing the killer's profile.
Doggett calls Reyes, and reveals that two more victims were found with the pattern bruising on their faces. Returning to the Bureau, she is congratulated by Agent Fordyce for her work. Reyes' revelation of her "special insight" into the case during the debriefing is met with disbelieving silence.
Vicki Burdick calls, but is murdered by Mad Wayne before she can reveal what she discovered.
As Scully performs an autopsy on Burdick's body, the patterns around her are all related to the number six. The pattern left on the victims' skin turns out not to be zeroes, but sixes.
After Scully and Reyes finish looking for evidence in Burdick's office, they ride the elevator with Mad Wayne. Scully notices the ring on Wayne's finger and draws her gun, but the elevator doors close.
Scully and Reyes use the stairs, and end up in the hotel garage. Suddenly, a car pulls away, a mechanical gate closing behind it. Scully and Reyes realize they're trapped. They search the garage, and discover Mr Burt. He claims he is waiting for a friend, with whom he was to play checkers. With little else to do but wait, the agents busy themselves playing checkers with Mr Burt.
Scully notices the colours red and black on the checkerboard. She stares at Monica's hair, and then touches her own red hair. As the killer strikes in threes - in the order of blonde, red head and brunette - Scully wonders if she and Reyes are the killer's next target. Mr Burt wonders if the numbers are helping the agents catch the killer... or if they're helping him not get caught.
The agents notice a figure watching them from behind a parked car. Suddenly, the lights go out. As Scully heads for the breaker box, Monica tracks the mysterious figure. Suddenly, Mad Wayne jumps out of the darkness and a struggle ensues. But the stairwell door flies open and a dark figure emerges to fire three shots, killing Mad Wayne. The lights come back on,
revealing that the shooter is Agent Doggett.
Doggett tells Reyes and Scully that something in the killer's pattern made him realize that they were his next victims. Moments later, the agents realize that Mr. Burt has vanished. Later, Scully asks Reyes about her numerology. Reyes tells her she's a nine. But when Scully asks about the mysterious checker-playing man they met in the garage, Reyes responds, "God
knows."
Back at the hotel, a festival parade gets underway. And as the camera zooms out, we see a bird's eye view of the city, and the lights form a familiar face: That of Mr Burt.