I'm a librarian who loves anime, manga, and reading a wide variety of genres.
One of the girls has disappeared, but hardly anyone's worried yet - mostly they're just arguing (over who's better, boys, the food, etc.). It's incredibly tedious.
I figure the cars they arrived in are a loss as well. When they got there, a guy dressed as a ranger told them he'd park their cars, and they just gave their keys to him (are they so used to valet parking that this didn't seem strange to them?). At any rate, it's looking more and more likely that the ranger was no such thing.
Now it's time for the flashback to That Night, the original slumber party that resulted in one death and one serious injury.