When an innocent deformed boy drowned due to the neglection of his summer camp counselors, when his mother took revenge on the counselors of the camp, when she was beheaded in the process. Oh yes, when Jason Voorhees rose from his watery grave to avenge his mother's death, evil was paying attention.
When a woman of God was locked in with the poor souls she was trying to help save at a mental institution, when they raped her numerous times, when a child was born from this, when he grew up and slaughtered many young children. Yes, evil was paying attention when the parents of those children burned Freddy Krueger alive.
When one Halloween night, a family was forever changed, cursed, when the innocent son took a knife and killed his older sister, when he sat in a mental institution for years, when he broke out years later, evil was paying attention the night Michael Myers came home.
An innocent child, who tragically died due to the neglect of those whose care he was in. His mother, driven by grief, killed while killing those she thought responsible. That child, now an undead force, killing all who dare come near that camp. A monster, born from sin, evil all his life, who now resides in the dreams of his victims, killing them at their most vulnerable. These circumstances, however different, led Jason Voorhees and Freddy Krueger to the same end: they were each endowed with an evil that even death could not extinguish.
And then there's Michael Myers. No apparant circumstances that led to his evil being awakened. An anomaly, one day, he just was. But unlike Freddy and Jason, Michael has not even tasted death.
In a world where logic reigns, how can these supernatural forces exist? And what's more, as they do exist, they can't remain apart forever. As chance would have it, Freddy found Jason in Hell. Its just a matter of time before Michael is drawn to them too.
Three forces of evil, all born of different means, all tied together by the evil that sustains them. The Unholy Trinity.