The demo puts you smack-dab in the middle of the fight - you must protect the citizens of Highwall, one of the last remaining havens for survivors of WWIII from the hillbilly mutant freaks trying to enslave them.
In a post World War III world, you certainly are better off dead. Survivors are living in constant fear of being murdered or enslaved by blood-thirsty gangs, renegade military units and monstrous mutants.