In the remote mountains of Scotland, in high-tech bunkers in South Dakota and in the lush valleys of New Zealand, small groups of determined men and women are getting ready.

They are environmentalists who fear the ravages of climate change; billionaire entrepreneurs dreaming of life on Mars; and right-wing conspiracists yearning for a lost American idyll. One thing unites them: their certainty that we are only years away from the end of civilization as we know it.

Not unconcerned himself by the possibility of the end of days, Mark O'Connell set out to meet them.