The kids made it to the Minerva location.  They survived the forest and the plains and have entered the underground sanctuary, where instead of finding Minerva, they find a an “old” geezer who just wants them gone.  Bu the kids are not giving up.  They are going to survive, and they are not going to let one adult stop them.  This was a great addition to the series.  It shows how hard it can be to survive on your own, and what long term loneliness can do to a soul.