Seven university friends go in search of a mysterious underground facility in the hills and, arriving late in the evening, encounter a family of three who have become lost walking in the same isolated region. The ten of them see no choice but to stay underground until morning, only for an earthquake to trap everyone inside. A means of escape exists, but requires that one person stays behind, trapping themselves underground where they might be lucky and not starve to death: instead, they may drown in the rising water filling the building from below. And so, naturally, one of the group is murdered. But why now? And, of course, whodunnit?