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 a more mysterious menace afoot?