Aang and his friends have finally reached Ba Sing Se, only to discover that the city is under attack from the Fire Nation, led by Azula, Mai, and Ty Lee, who are using a giant drill. Initially, the commanding general in charge of fending off the attack is reluctant to accept the team's help, but after Mai and Ty Lee quickly dispatch the general's "Terra Team", he changes his mind. Seeing that outer attacks have no effect on the drill, and using Ty Lee's chi-blocking as inspiration, Team Avatar goes inside the drill to take out its weak points and hopefully bring it down before it breaches the city's outer wall.