The movie is a documentary about life 12 years after a deadly plague wiped out most of humanity. The cause of the plague is never revealed, nor why the people survived. The filmmakers are in San Francisco, which now has a population of 186. They visit many of the survivors to see how they have coped and how they have survived. Some have become traders, some scavengers, some are isolationists, and others live together in a commune. All of them are dealing with life ever since the world ended.
"Mad Mark", the pyromaniac who dealt with the apocalypse by burning down homes and warehouses full of food and necessities, is banished from the city and threatened with death if he returns. He does return, and is murdered a short time later. Adam the Engineer (played by a pre-Mythbusters Adam Savage) is the prime suspect, but he claims he's innocent, even though he also says he would have liked to kill him. His killer is never found, because the other survivors are also glad he's dead and don't want to know who killed him.
Santosh is leading the filmmakers and other hikers through the mountains to see life outside of San Francisco. For some, this is their first trip outside of the city since the plague hit. He is shot as they approach an old ranger station by an unknown shooter. The others carry him down the mountain to safety, and as they decide whether to carry him back to the city or go ahead and get the city's only doctor to come to them, one of the others shoots him to death to put him out of his misery.
The film ends with a screening of the movie in an old theater. All of the survivors who are profiled in the film are present. The conclusion is that life will go on, but humanity will have to return to a pre-Industrial Revolution lifestyle in order to survive. That is, life without electricity and everything else we take for granted. This will include growing their own food, building their own homes and necessities, using water, wind, and solar power to run machinery, and so on. Since the children of today are already used to this, it shouldn't be too difficult for them once they are grown.