In the world of Enclave, we find a society made up of groups of children and young adults, living underground in subway tunnels, after something has happened to mankind. A rule-and-order based society, they trade with their nearest neighbors and hunt in the tunnels for food. Life is hard, death is a constant threat and most don't make it - the oldest in their tribe is 25 years old.
There is also the threat from "freaks" - zombie-like adults who want to kill and eat them. The exact nature of the calamity that has befallen the planet isn't known, this is just the world they know. Eventually, a group is forced to leave the relative safety of their enclave to travel above ground - a world populated mostly be gangs who are pretty violent.
Enclave doesn't specifically identify its location (that I can recall) until near the end, except to say that it's a U.S. city, but I couldn't help feel like it would be at home in the Enemy universe, only a slightly more sanitized version. Enclave is tamer. Not boring, but a little calmer, a little less stressful, a little less fearful. And I'm fine with that. I'm curious to see how the rest of the trilogy pans out.