Not long after the Prague Spring in 1969, Julia, a teenager living near the Czechoslovakian border, is persuaded by her peers to go down into the tunnels that have remained along the border after World War Two. Julia begins to regularly cross over to Czechoslovakia, where soldiers are building a fence to prevent defections. She becomes friends with a middle-aged soldier, who helps her remain undetected. One day, on her way to the other side, Julia realises she has lost her friend forever.