Mulder and Scully investigate the death of Dr. Ronald Surnow, an aeronautical scientist, who was developing a jet engine that could double supersonic speeds using half the fuel. Surnow was sucked into the engine when he became trapped inside a wind tunnel. Surnow's colleagues, Drs. Keats and Nollette, tell the agents that another member of the team, Arthur Gamble, died in a car accident not long ago.
     The agents interview Roland Fuller, a mentally-challenged janitor, who was the only other person inside the lab at the time of the incident. Mulder is intrigued by Roland's ability to manipulate complex numbers. But his attempt to link Roland's handwriting with some unidentified equations on a blackboard at the lab prove unsuccessful.
     Shortly thereafter, Roland murders Keats by forcing his head into a vat of liquid nitrogen and smashing his frozen skull. The agents investigate, and realize that after Keats was murdered, the perpetrator gained access to a computer file that belonged to the late Arthur Gamble. During a visit to the cryogenics lab where Gamble's head is preserved, they also discover that Gamble and Roland are identical twins.
     Mulder arranges for constant surveillance of Nollette-who is most likely to be the next victim-after Roland disappears. Mulder speculates that the twin brothers share a psychic connection, and that Gamble is controlling Roland from the Netherworld. Nollette overhears Mulder's theory and sabotages Gamble's cryogenic unit.
     Roland gains access to a computer terminal and completes a simulation that pushes the jet model past Mach 15. Nollette suddenly appears, gun in hand. He thanks Roland/Gamble for solving the equation, allowing him to take credit for the work. Roland becomes enraged and overpowers Nollette. He locks the scientist inside the tunnel and starts the engine. Mulder and Scully gain access to the room and ask Roland-not Gamble-to remember the access code that will shut down the engine. Roland recalls the code and disengages the machine.