Once the Fire Nation armada arrives , Zhao begins his attack while Zuko infiltrates the tribe on his own , capturing Aang while he entered the spirit world to find the dragon spirit to give him the wisdom to defeat the Fire Nation . Soon , the Fire Nation arrives and Zhao begins his attack while Zuko begins his search for the Avatar on his own , capturing Aang as he enters the spirit world to find the dragon spirit to give him the wisdom to defeat the Fire Nation .