The end of the world has been and gone.

There was no one great natural disaster, no all-consuming world war, no catastrophic pandemic. Only scores of storms, droughts, and selfish regional conflicts. Humanity was not granted a heroic end. Instead, it bled to death from a thousand cuts.

But where Earth fell apart, Mars pulled together. Engineered men and beasts, aided by Bees - an outlawed distributed intelligence - survived through co-operation, because there was simply no alternative.

Fast forward to today. A signal - 'For the sake of what once was. We beg you. Help.' - reaches Mars.

How could they refuse? A consortium of Martian work crews gather the resources for a mission: a triumphal return to the blue-green world of their ancestors. And now here they are - three hundred million kilometres from home.

And it has all already gone horribly wrong.