As I mentioned in my review of Earth 2, the Supergirl and Robin (Batman and Catwoman's daughter) of that world got pulled into a wormhole into our world. Well, the main DC Universe. Which last I checked, is not our world.
Since they realize they can't approach the people they knew other version of, they decide to start new lives for themselves, as Power Girl and Huntress. Power Girl is a socialite who funds research into ways to get back to their world and Huntress focuses on stopping crime.
They are good friends and I enjoyed seeing their relationship throughout the book. I don't know if I'd pick up another volume, but I won't rule it out.