Real-life MAFIA game with only 9 students left, who is the killer?

This is part 3 of the K-drama "Night Has Come" Her best friend was hiding a secret from her. The high school students are stuck in a game of real life mafia. They’re trapped in a secluded mountain youth center, no cell service, no ability to leave, and everyday they’re forced to play the game or else they die. Yuni was in this with Wendy. That’s her best friend. That’s who she was going to get through this with. They were going to get through this together… Except Wendy is part of mafia. In order for Wendy to live Yuni must die. In order for Yuni to live Wendy must die. Will the high school best friends who have been with each other through everything - finally turn on each other?