16 Days 'til the Rest of Your Life (2005)

Andy gets back from holiday and is greeted by his girlfriend and friends. But Andy has a surprise for them ... his fiancée. The friends are stunned... Their jealousy turns to anger, their anger leads to paranoia and paranoia pushes them to reach the only logical conclusion: That Andy's fiancée ... Is a demon. But how do you go about killing your best friend's fiancée without alerting him.. ? Or his family...? Or the other wedding guests...?