It starts innocently enough. Four kids - three girls, one boy - are at one of their houses, playing games. One of them has read about "Bloody Mary" and the idea that if you look into a mirror and say her name thirteen times, she will show you the future. Some legends say she'll show you your one true love or a skull to mark your death within five years. Others say that conjuring Bloody Mary will bring her into your world.
Both sets of legends are true. The kids go through with the act, saying her name thirteen times. One girl looks in the mirror and sees her longtime crush. One girl looks in the mirror and sees the boy in the group. But she pretends to see something else. One girl looks in the mirror and sees a girl she's never seen before but can't get out of her mind. And the boy . . . he sees a skull. But he pretends to see something else. They try to laugh it off. And mostly they forget about it. Or at least they don't talk about it. Yes, over the next few years, whenever they look into a mirror, it's like there's always another figure standing in the background, getting closer.
Just short of five years later, the four of them are no longer friends, having gone on separate paths. The girl whose house it was has always tried to avoid the mirror they used - because she always sensed someone in the background. One morning as she's passing by, she sees much more than her own reflection - it's a scary figure taunting her. She startles and breaks the mirror. When the pieces are put back together (barely), the figure is gone.
That day in school, a new girl arrives. Her name is Mary . . . .