I don't know, but I really hope it is quite soon, because I don't know what i'll do if they never make it. It was really quite rude to tease all the fans like that. Making a movie for City of Ember and then stopping. Tsk Tsk. Shakes head in dissaproval
They recently announced that they will not be filming The People of Sparks; they stated that since the reviews, ratings, and earnings were incredibly low, making a sequel wouldn't be worth it.): At least we have the books!
