The Rushing Conflict
He became addicted to the rush of the sensation and began causing trouble with it. Anthony Reed was somewhat of a friend of Harden's who Harden was going to introduce to the cave with the speed-giving property, along with his perhaps girlfriend, Chastity Raines. However, they were stopped by Deputy Ronald Foster. Harden attacked Foster with incredible speed, bludgeoning him to death with a flashlight so forcefully that his entire head caved inward. Mulder and Scully were called in to investigate, even though Tony Reed was the obvious suspect.
Eventually, Mulder began to suspect that superhuman speed was involved when the flashlight was stolen from an evidence locker. Dr. Charles Burks analyzed security footage and was able to identify a blurred object in a single frame that had the local high school's colors on it. Mulder also found bits of melted rubber at the scene.
Meanwhile, at the school, Harden completed a midterm exam for his nemesis, Mr. Babbitt, in a few seconds. Nevertheless, he failed the test despite getting every answer correct and was accused of cheating. Later that day in the school cafeteria, Harden humiliated Babbitt by tripping him and spilling his lunch. He then attacked Babbitt and launched him into a wall with a lunch table. Already dying from nearly being severed, Babbitt was killed when Harden threw a chair at his head, blowing it apart.
Tony Reed and Chastity Raines decided it was time to stop Harden on his spree of killing. Even his father, who had aggressively pursued prosecuting Reed, came around upon discovering that his son had the flashlight used to kill Deputy Foster. Harden confronted his father and injured him, but was taken away at gunpoint by Reed. Harden was then taken to a hospital, and his body showed intense signs of stress that were due to his superhuman speed. Against her better wisdom, Chastity helped Harden leave the hospital so he could recharge at the cave. She and Tony made their way to the cave, hoping to get their first while Harden confronted his father.
Harden arrived and nearly killed Reed. Raines was able to take a gun from Harden that he had taken from his father and shot him. Realizing her life was never going back to normal, she stepped in front of the bullet while it appeared - in her ultra-fast state - to be moving very slowly through the air. Both she and Harden were found dead by the time Mulder and Scully arrived. (TXF: "Rush")