Mankind can no longer reproduce because of gene manipulation aimed at making life longer. The clones ruling the bottomless underworld may have become fertile. Parton is selected to go on a mission through a subterranean labyrinth crawling with monsters to secure humanity's future.

1,042 years before JUNK HEAD, a robot named Robin escorts a human commander on a mission to the underground city of Carp Bar.

In the distant future, mankind begin research on clones that live underground in search of lost genetic information.