The series "Black Knight" is a Korean science fiction drama set in a future world. By 2071, our planet has become so polluted that the air has turned into toxic gas. People all over the world start dying in large numbers, but by the time scientists manage to stop the tragedy, only one percent of humanity survives. The survivors breathe through respirators and are subjected to a strict social hierarchy. The only saviors for them are the Knights - couriers who venture out from their shelters into the outside world.