Creature of the Night

My short story for the CreatureFeature contest

Nikki believes someone or something watches her at night and only appears where it's dark. Because of that she never sleeps with the lights off.
One day Courtney, Nikki's enemy, invites her and her friend, Amber, to a party. This leaves them cautious since Courtney has never been remotely nice to them before. When they arrive at the party everything seems normal, however once 12:00 hits people start to die. It all starts with the flashing of the lights then one more is gone. Who is doing this? Is Courtney behind this or is there something more?