On prom night ten years ago, a group of drunken friends go too far when trying to scare a couple of their fellow classmates. After accidentally killing one of them, they decide they have to kill the other one in order to cover up the crime and protect themselves and their futures. Now, ten years later, as they start coming together for their high school reunion, each member of the group is being picked off one by one by a ghostly killer as some sort of revenge from beyond the grave.

Thanks to an auto accident, a parasitic alien manages to get into a hospital. It quickly moves from the crash victim into a candy striper. Among the patients at the hospital are some rather short high school basketball players. It is through them that we watch the events unfold. The infected, or inhabited, candy striper becomes predatory. She goes after men for sex and after women to spread. Infected women develop an incredible sweet tooth and devour anything sweet they can find. The horror then spreads. As the horror takes over more of the hospital and the CDC locks it down, the basketball players and a few friends do everything they can to try and get out of the hospital. But soon it becomes evident that the problem has spread too far. Now if they manage to escape it will only be to delay the inevitable if they cannot halt the spread of aliens before they get out and take over the whole world.