How did humanity fair over those blighted two centuries? Lucy, one of the lead characters, has no clue. She has lived her entire life inside a subterranean vault,  where every need and want has been satisfied while generations and generations await the day when it is safe to surface. When a crisis forces Lucy to venture above on a rescue mission,  she finds that the planet above remains a hellscape crawling with giant insects,  voracious mutant animal “abominations,”  and a human population of sunbaked miscreants. Lucy is nice, but Lucy is naïve.

- Taken from Vanity Fair Article

Note: The way I characterize Lucy likely won't be how Ella Purnell portrays her.

This is my take on Lucy