Why are kids' movies the only ones allowed to deal with real grown-up issues? City Of Ember, opening today, reminded me of the allegory-rich Wall-E. Not least because it talked about issues like scarce resources and the cushiony softness of propaganda. It's such a relief, after watching a thousand allegedly "grown-up" action-adventure movies, to watch a film that actually talks to me like I'm 12, instead of four. Spoilers ahead. In City Of Ember, based on a bestselling series of young-adult novels by Jeanne DuPrau, it's the distant future. Some kind of unspecified (in the movie) calamity has rendered the surface of the Earth uninhabitable. The last survivors of the human race huddle in an underground city, but they're running out of supplies and the city's generator is failing. Soon enough, the city won't support life any more. It turns out the people were supposed to leave the city long ago, but the city's incompetent leadership lost the instructions. So it's up to two plucky kids to discover the way out of Ember.

In some ways, it's quite similar to Wall-E: humans have abandoned the surface of the Earth for an artificial environment, because we trashed Earth. And now it's time for humans to return to the Earth's surface, but those in charge want to preserve the status quo. So it's up to two kids/robots to lead the way. The only difference between Wall-E and Ember is that in Ember, the humans are starving to death instead of living in luxury. Thinking about Ember, I was reminded of something Steven Moffat, the new showrunner of BBC children's show Doctor Who, told me when I interviewed him in July:

The misconception about children's fiction is that it's lightweight or fluffy. It's about really big and important things. It's adults who like light and fluffy. Everything is big and important to a child, [so] their stories are about big and important events.

You don't have to dig terribly deep in Ember to find a wealth of political allegory. It's all right there on the surface, like it was in Wall-E. The thing that's great about Ember is that its story of post-apocalyptic survivalism feels like a tangible thing. You practically smell the fug of the city's generators and the rot of its ancient timbers. You can feel the dirt and tar under your fingernails. That makes the story of a city that's running out of resources much more compelling and hard to forget. Director Gil Kenan said in an interview recently that he wants you to walk out of Ember and feel surprised and relieved that there's a sky overhead. Which is exactly the feeling I had.

Kenan and production designer Martin Laing built the entire city, more or less, in the hangar where the actual Titanic was built. And this fiendish over-building pays off, because Ember feels like a real place. It's a cliche to say that a place becomes like a character in a story, but it's kind of true this time around. Another reason why Ember might have a bit more oomph than Indiana Jones 4 or Incredible Hulk: Bill Murray has the time of his life playing the corrupt mayor, who sees his job as making people okay with a doomed status quo. At some level, the mayor knows everybody is fucked, but he has no answers. So his version of leadership is to administer slow euthenasia to his citizens, keeping them optimistic long enough to cushion the blow of their inevitable extinction. He promises to assemble a blue-ribbon commission to investigate the city's power outages, and meanwhile stockpiles supplies in a hidden bunker for when things go all the way south.

Which brings me to another way Ember ruled: it showed how nice and cozy political propaganda can be. People always talk about hope being a brave thing — the phrase "the audacity of hope" is a bit shopworn at this point — but actually, hope is the coward's way out. When the sky really is falling, hoping for the best is just a coping mechanism. The people in Ember have a sort of vague theology about the Builders, who created the city and will come back to save everyone. The townsfolk also believe that there's nothing but darkness outside the city, and the surface of the Earth — and the sun — don't really exist. Propaganda and religious dogma blend together into a warm slurry.

I haven't even talked about Saoirse Ronan yet. The good news is, she's pretty great in a role that could easily have been annoying or worse. She's a much better detective this time around than she was in Atonement. She and costar Harry Treadaway compile a series of clues that mostly fall into their laps, but they also make a few clever deductions and put the pieces together. I love detective stories, including kid-detective stories, and any movie that blends genres is automatically on the right track as far as I'm concerned. A post-apocalyptic Nancy Drew story? Sign me up! The thing that's moderately clever about the kid-detective plot is that a small act of rebellion touches the whole thing off. Both Lina (Ronan) and Doon (Treadaway) receive assigned jobs from the state in the Day Of Assignment. Murray's mayor pulls job assignments out of a bag in front of a mostly empty auditorium, and gives each kid the job that he or she will have for the rest of his/her life. There's no social mobility, no aspiration, just the job you're assigned. Lina and Doon both receive the absolute worst jobs for them: she's assigned to the city's pipeworks, and he's made a messenger. Even though these assignments were announced in front of everyone, they agree to swap. And it's thanks to that trade that both kids start noticing the clues that lead to a way out of the city.

Right after I watched Ember, I got into a debate with another critic, who was there to review it for a film site. She felt like the film was religious propaganda, because the kids find the way out of the city by having faith and persevering in the face of obstacles. They become the saviors of Ember and lead everyone out of the darkness into the light. I felt like the movie was actually saying the opposite: the two kids save the city precisely because they don't have blind faith. Instead of taking the received wisdom and believing the city's leadership, they observe the world around them and look at actual evidence. Their emergence into the light is a triumph of reason over superstition. I don't have a definite answer as to which of us was right. But the fact that two adults could have a spirited argument about the political meaning of this film — just the way conservatives and liberals have both claimed Wall-E as a conservative or liberal parable — seems like a good sign to me. Oh, and I almost forgot. The major addition to the film that wasn't in the novel appears to be a giant tentacle-faced mole that stalks our heroes through the tunnels. It didn't bother me, and it was kind of a crazy surprise in the middle of an otherwise semi-realistic story. But you can see it for yourself here, and decide if you think it mars an otherwise great film.