Fifty-seven years ago, the alien race Nonsuch attacked Earth, killing 95% of humanity. Survivors live underground, except for soldiers who serve 100-day tours at outposts. Sum1, a new soldier, is dropped at Cerberus outpost. He activates the system through DNA identification and begins his duties to defend against the Nonsuch, monitor cameras, and take stragglers to Exilium. Sum1 reports to his commander and is reminded of his responsibilities.