After defeating Katara in a battle , Zuko captures Aang as he enters the Spirit World to find the Dragon Spirit to give him the wisdom to defeat the Fire Nation who tells him to let his emotions flow like water .
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 .