This documentary focuses on borders, those boundaries invented by humans, which can appear, disappear or change suddenly. Some borders follow the course of a river, coast, or mountain range; others are drawn in straight lines. Some are wide open, and others are closed by walls and armies. But whether they are dangerous or not, humans have always crossed them: to explore, take shelter, invade, trade or find a job or a meaning in life... As for birds and fish, they don't care about borders, such as airwaves, air or pollution.