On an ordinary Saturday Afternoon in Suburban California, a nervous young woman (Melanie Lynskey), housesitting for friends, has organised a slumber party for the women at her office. However, only three guests arrive: her cynical friend (Sheeri Rappaport), the office outcast (Mary Lynn Rajskub)... and somebody who may or may not be the serial killer who has been terrorizing the local community all summer. In short order, the girls see a black-clad figure moving outside, hear footsteps on the roof, then discover that both the electricity and the phone lines have been cut. They try to temper their fears with scepticism... until the blood starts flowing.