A mystery teen drama that takes place when a class of second-year high school students is suddenly forced to play mafia games in real life during their retreat. The drama will draw out the intense psychological warfare between the students as they go into survival mode. Students in the 2nd grade 3 class at Yooil High School go on a field trip. There they are forced to participate in a mafia game of death, and they struggle to survive. Lee Yoon Seo has excellent observation and reasoning abilities, which she uses to try to escape. Kim Jun Hee is the class president with a strong sense of justice and responsibility. Oh Jung Won ranks first at school academically, but she is an outcast and a loner. To survive, she must work with the other students.