A technologically advanced society, long forgotten in the world's history has a crisis and develops a plan to bring people BACK in time to help them. Time travel, and the problem the society faces aren't original ideas. But going back in-time to a society more advanced then your own gives the tale a unique twist. The novelty of this is lost a little purely because the society is so advanced. It is easy for the reader to think "future" instead of "past."