Directive 17. Next, #4

In a contaminated wasteland, Rachel Wheeler and an intelligent mutant baby find shelter in a silver city where neither belongs. As the dwindling human race desperately fights to survive, they're forced to adapt to the mutant technology and the new race that threatens them with extinction. But the hostile environment poses other threats as well - strange creatures and giant predators roam the wilderness, fueled by the mysterious radiation leaking from the advanced cities.
Rachel's friends come to the rescue, but they discover she's crossed a border from which no human ever returns. But something else might.