A group of bored rich teens organize an illegal rave in the network of catacombs beneath the Munich central train station. When a fire suddenly breaks out in the tunnels, there is a stampede and the party-goers try to flee, but they don't all make it out. The following day it turns out that there are dozens injured and three missing youths, including Nellie's brother, Max. With her best friend, Janosch, Nellie sets off in search of him, but they are unaware that beneath the city streets dwell the "Invisibles," a people cast out and forgotten by the world above.