Avatar Aang asks his friends to help him honor Yangchen''s Festival - one of the highest Air Nomad holidays, which hasn''t been celebrated in over one hundred years. But cryptic visits from the spirit of Avatar Yangchen herself lead Aang to discover a jointly owned Fire Nation and Earth Kingdom refinery - operating on land sacred to the Airbenders! Is this the cause of the pollution Aang finds there or is something more mysterious happening?