The struggle at the center of City of Ember, another treat from the maker of Monster House, is one for the good of all mankind. But what were the denizens of this world running from when they first trekked underground? Two hundred years after their mucky netherworld's inception, the ever-hiccupping generator that keeps the lights on in Ember threatens to go forever kaput. It's up to Lina Mayfleet (Saoirse Ronan) and Doon Harrow (Harry Treadaway) to decipher the clues left inside a mysterious box and usher their people — like Obama or Moses, take your pick — toward deliverance. Backstory and motivation are almost nil here, but director Gil Kenan reveres the abstract tenor of Jeanne DuPrau's acclaimed children's book, understanding the postapocalyptic story as an allegory for the determination of humanity against the forces of darkness — whatever or whoever they may be. Its look suggests a twee City of Lost Children, but Kenan isn't hung up on style alone, equally and voluptuously reveling in artifice and the courageous will of Ronan and Treadaway's hopeful foot soldiers. The story subtly evokes Rand and Scripture, colliding secular and spiritual values, and, as such, appeals to the blue- and red-minded alike.