After getting tickets for the ferry headed to Ba Sing Se, the gang meets an old friend. They skip the ferry ride to help some refugees, one of which is going to have a baby, get to Ba Sing Se. They must lead the refugees through the Serpent's Pass, a dangerous mountain-side path surrounded by water. After arriving at the great wall of Ba Sing Se, Aang and the gang discover that the Fire Nation has constructed a great drilling machine to penetrate the wall. The drill is also followed by an army of Fire Nation troops. Also, Zuko and Iroh are having trouble hiding the fact that they are both Firebenders. (thetvdb.com)