Warning: This review contains spoilers
The premise is that there are a bunch of superheroes in most major cities, a dark group and a light group. Of course, no one in the regular world knows about it. It's a little bit like X-Men only not as open.
I liked the book. It was a fun read even if there were times when the characters seemed particularly dense. The first time Joanna mentions she had a child and the Zodiac mentioned that they operate under a matriarchal society she should have made the connection. I did. And it's not like she hadn't been thinking about the kid.