Of the 9 people, who is it okay to die - who should die?

Shuichi visits an underground building deep in the mountains with his club friends from the university. They accidentally wander into an underground building with a family of three and spend the night there, but an earthquake occurs in the middle of the night, blocking the door and causing water to pour in from underground. To escape, one person must stay behind. Then a murder occurs, and if the culprit is not identified, they would all be dead. The brutal search for the culprit, with a time limit of about one week, begins!

Based on the novel written by Yuuki Haruo.