A trip into subterranean Berlin goes horribly awry for a group of curious young urban explorers. After their guide is injured, two members of the party seek help while the others stay behind. When an ex-East German border guard appears with an offer to help, the exhausted explorers agree to follow him. Later, by the time they realize they have wandered into a trap, it's already too late. Now, if any of them hope to see daylight again, they will have to fight for their lives in total darkness.