The Sanctum, the brainchild of gregarious security consultant Greg Fuller, is a luxurious, self-sustaining survival condominium situated fifty feet underground in a remote location in rural Maine. It's a plush bolt-hole for the rich and paranoid - a place where they can wait out the apocalypse in style.

When a devastating super-flu virus hits the States, several families race to reach The Sanctum. Among them are committed preppers, people who have invested a great deal of time and money preparing for any apocalyptic scenario. All the residents have their own motivations for buying into the development. All are hiding secrets.

And when the doors lock and a death occurs, they realise the greatest threat to their survival may be trapped in the Sanctum with them.