Imprisoned

This is episode 6 of Avatar: The Last Airbender.

Aang and his group are hungry and are looking for food. In their search, Katara stumbles upon a fledgling Earthbender named Haru who immediately runs away. The party follows after him into a village where everybody is suspiciously quiet; the reason is revealed quickly enough when Firebenders walk into the town looking to tax the Haru's family. Indeed, the town is an occupied Earthbender town that is of strategic interest to the Firebender Nation for its rich coal deposits; all the martial Earthbenders (including Haru's father) have been long imprisioned, and the practicing of Earthbending strictly forbidden. One day, Haru and Katara are walking by the coal mines when a shaft collapses; Katara coaxes Haru to Earthbend to save an old man's life. Not surprisingly, this old man is a spy for the Firebender secret police, who raid Haru's house at midnight and carry him off to a rig. Katara wants to follow to rescue Haru, so she has Aang use Airbending in conjunction with the mine shafts to convince the Firebenders she's an Earthbender (not a Waterbender); this succeeds and she is carried off to the prison, with Aang and Sokka following on Appa. The prison is an iron rig, where prisoners have no access to any Earth; Katara's efforts to incite revolt fail initially. Aang infiltrates the area, uses the airbending trick to blow the rig's coal deposits towards the Earthbenders so they have a weapon to use, and a battle ensues between Earthbenders and Firebender guards. The Earthbenders break out, and Haru and his father say they won't keep Aang from his quest; they have to liberate their village. Of special importance is that Katara lost her mother's necklace in the prison; the episode ends with Prince Zuko striding into the prison ruins only to pick it up.