Cassandra Morphy

Paige grew up in the undercity, the remnants of the old city of London, in the shadow of New London, high overhead. The sound of zombies at the gates were a constant reminder of how close her death could be. Like most morlocks in the undercity, Paige was an NI, non-immune to the zombie virus that had taken over the world. The immune live in the upper city, focusing on spreading their immunity into the next generation of humans.
But Paige had something thing that the other morlocks didn't: a ticket up the elevator and a job waiting for her when she got there. Mistress Gilbert, Paige's new boss, didn't have much patience for morlocks. They were beneath her, both literally and figurative. Beneath society and the rules that had governed it since the fall of the world. As long as the morlocks remember their place, sticking to their lower standing as NIs of the uppercity, she would let them be.
However, the moment that they step out of line, she would be the first to call for them to return to the undercity where they belong.