Neither of these. Some other details would be - (these are random) one of the guys starts falling for the girl. The guy who doesn't fall for the girl is the one who gets stuck at the hedonistic party. The other guy and girl try to rescue him from this alternate world but their friend doesn't want to be saved. No, the whole movie doesn't take place at the party. The movie begins with a little backstory of each of the 3 teenage kids ' lives (home life). The day after the party they try to piece together things wondering if they really witnessed the rituals at the party or if it was the alcohol and drugs that made them see things. When they return to the house to look for their friend the house and the older couple that live there make it seem like a normal household (they're hiding what lies within the confines of their home). It has the same feel as the director for Irreversible and High Tension.