The X Files Season 8, Episode 17: Empedocles

• When some of us are vulnerable we can let pure evil come inside us
• Mulder:  And I began to think about evil like, like a disease. You know, that it goes from man to man or age to age. Most of us walk around thinking we're incapable of any acts of evil and we are. You know, we can stifle that momentary urge to kill or to hurt. We have some kind of immunity to it. But I think it's possible that there's... an occurrence in somebody's life, a tragedy or a loss that leaves them vulnerable, hurts their immunity to evil, and all of a sudden at that point in their lives when they're weakened, they're open to evil and they can become evil