After the outbreak, every apartment block, hospital and mall became a vault: full of supplies, full of the dead. Survivors go in one floor at a time, with a rifle, a backpack and a way out.

Your gun fires on its own; you choose where to stand, when to push and when to back off. Cabinets hold scrap, medicine and valuables, reinforced doors hide the best rooms, and some floors wake the horde.

On the roof waits a mutant boss. Kill it and hold the roof until the helicopter lands, or walk back down to the extraction point with whatever you could carry.