You're Invited — Alicia Dean

Party til you drop…Morgan Michaels and her friends invite an unpopular girl from their high school to a Halloween party as a joke…but the joke backfires, and the girl ends up murdered.One year later, they receive an invitation to a mysterious Halloween party. It's all fun and games at first, but Morgan soon discovers there's a psycho in their midst, and he's slaughtering them one by one, using a prop from each of their costumes.Now the killer is in hot pursuit of the remaining survivors. Can they unmask the maniac before they, too, meet an untimely end?