Based on Philip Reeve's steampunk-ish YA novels, this sci-fi fantasy takes us to post-apocalyptic Europe, devastated by a catastrophic world war. Long-destroyed cities have been rebuilt at sea and in the air. But on land, the biggest cities have been reconstructed as towering, tank-like monstrosities crawling their way across the landscape and waging war on smaller, slower towns. In the mobile metropolis of London, two young people (Hera Hilmar, Robert Sheehan) meet and try to stop a conspiracy involving an ancient weapon of incalculable power. The setting is imaginative, but the story is cobbled together from a variety of familiar sources.128 minutes PG-13.