S3E12 · Book Three: Fire - Chapter Twelve: The Western Air Temple

Complete story — includes the ending

Zuko approaches Aang and his friends at the Western Air Temple, with the intention to join their group and teach Aang firebending. He desperately tries to prove to them that he has changed for the better, however they furiously reject Zuko due to his past actions. After he leaves, Toph challenges the others for dismissing him so quickly when Aang is in desperate need of a Firebending teacher. She eventually decides to speak to Zuko herself, but she accidentally startles him in his sleep, causing Zuko to reflexively firebend at her and burn her feet. Toph crawls back to the temple for help, where Sokka decides they must go after Zuko in retaliation. Team Avatar is nearly killed upon the sudden arrival of Combustion Man, but Zuko intervenes and affects his aim just enough to save them. Sokka defeats Combustion Man by hitting him in the third eye with his boomerang, causing the assassin to blow himself apart. While the group does allow Zuko to join them, they are still reluctant and skeptical. An embittered Katara warns Zuko that she will kill him if he betrays them or hurts Aang again. Note: This episode first premiered on December 14, 2007, in Canada.