The scene opens with Aang Toph, Momo and Katara enjoying a short refreshing break in a pool of water at the base of a waterfall while Sokka reviews the maps they acquired from the Spirit Library. After accidentally soaking the maps with a waterbending bomb (similar to doing a cannonball in a pool), Katara uses her waterbending to extract the water from the maps. The group then huddles around the map to discuss which direction they should go – the Serpent's Pass appears to be the most direct route. Just as they decide Serpent's Pass is what they will head toward, a group of three Earth Kingdom refugees approach and greet the gang. Hearing Aang's group's plans to go through Serpent's Pass (a route for only the desperate) the Earth Kingdom trio convince Aang's group to go to Full Moon Bay to take a ferry to Ba Sing Se.
After arriving at the hidden Full Moon Bay Ferry station, Katara is amazed to see how many refugees there are awaiting transportation. Unknown to the group, a ferry which has just departed has not only Uncle Iroh and Prince Zuko disguised as Mushi and Li, but also three former Freedom Fighters, Jet, Smellerbee and Long Shot. Jet manages to convince Zuko into liberating some food from the captain.
Meanwhile, back at Full Moon Bay, the ticket master refuses to allow the Cabbage Guy to bring on any vegetables as they may have parasites. Aang then approaches the ticketmaster and requests four tickets. She refuses as he does not have a passport, no animals are allowed and she refuses to believe Aang is the Avatar as she sees 50 a day. Aang backs away as Toph approaches with her family crested documents and the ticket master practically falls over herself to accommodate Toph by granting passage to the four of them (and allowing Momo as her seeing-eye-Lemur).
Just as Sokka is celebrating their score of the tickets, he's grabbed at the neck by a guard asking for tickets and passports. Not recognizing her until she kisses him on the cheek, Sokka is surprised by a clean faced Suki greeting them. As they catch up on old times, Suki is told of Appa's disappearance, the trio that was traveling with Aang's group calls up to them in desperation as their tickets, and passports had been stolen. Despite Aang's appeal to the ticket master, she will not allow the trio onto the ferry. Therefore, Aang decides he will lead them all through the Serpent's Pass.
As the group heads to the Serpent's Pass, Suki joins them although Sokka seems to have some misgivings which he doesn't voice. The group arrives at the Serpent's Pass and Katara reads the inscription on the post at the entrance stating they should abandon hope. As they head along the pass, they see a Fire Nation ship in the lake. Suddenly, the rock path gives way underneath one of the refugees, but Toph manages to save him. Unfortunately, the rock fall attracts the attention of the Fire Nation ship, which begins firing at the group. Aang deflects fireballs from the group, but one manages to make a hit. After pushing Suki out of the way of rock debris from a Fire Nation blast, Sokka is sure to be hit, but Toph earthbends a barrier to deflect the rock. Instead of thanking Toph, Sokka focuses on getting Suki out of harm's way. This rightfully annoys Toph, but she quickly follows the group. As night falls, Sokka again acts overprotective of Suki, which baffles her.
Back on the ferry, Zuko, Jet and Smellerbee sneak up into the captain's private food storeroom and liberate some food. Long Shot shoots up a line for them to escape, which is then pulled out once the group is back on the lower deck disguising the escape route.
As Aang looks out over the water, Katara lets Aang know it's alright to miss Appa. She asks why he's keeping his emotions in check and Aang replies that he didn't like how anger changed him in the desert. Katara encourages Aang to not give up on hope and attempts to give him a hug, but Aang simply bows and thanks her for her concern.
As Sokka is looking at the moon, Suki approaches him and comments on its beauty. She asks him why he's being so over-protective, he tries to explain about how he was unable to protect someone at the North Pole, and he doesn't want that to happen to anyone else he cares about. Suki, in a roundabout way, tells Sokka she has missed him and the two almost kiss, but Sokka claims he can't. Suki apologizes, but Sokka says it's not her fault.
As the ferry continues its passage to Ba Sing Se, Jet hands out food to other passengers, while Iroh comments that Smellerbee is an unusual name for a young man, Smellerbee says maybe it's because I'm a girl and storms off. Long Shot seems to calm her down. Jet sits with Iroh and Zuko and thinks about how great it will be to see the wall of the great city. Iroh says it is a sight to behold as he saw it once when he was a different man. Jet says he's going there for a new beginning and Iroh says to Jet, but appears to be directing the words at Zuko, that people deserve a second chance.
The next morning at the Serpent's Pass, the group hits a section which is completely submerged by the lake. Initially discouraged, the group is brought together as Katara tells everyone to get in a single file line as she parts the water for them to walk the path. Aang helps out and they create a bubble for them to walk in. Momo jumps into the water looking to catch some fish when suddenly something large swims by. The bubble is burst by the creature, Toph earthbends the floor of the path high enough to get them above the waterline. The creature circles them and then shows itself. As Sokka states, we now know why it's called the Serpent's Pass. Aang tells Katara to get the others to safety as he distracts the serpent. Katara makes an ice bridge for the others to cross and then heads out on top of the water to assist Aang. Sokka encourages Toph to cross the ice, but mid-way the serpent smashes the bridge sending Toph into the water. Suki rescues her, but thinking it was Sokka, who had called out to Toph that he was coming for her, Toph kisses Suki instead, an embarrassed Toph says "You can go ahead and let me drown now." Aang and Katara make a huge whirlpool spinning the serpent, which eventually gets knocked out as it hits one of the pass' walls. The group completes its trek to the other side of the pass and they see the wall of Ba Sing Se. Unfortunately for Sokka's smooth sailing plans, the pregnant refugee goes into labor. Katara takes charge again and designates jobs to everyone as they prepare to help the woman deliver her baby.
Jet tells Zuko that from the scar he knows who he is, which immediately put Zuko on the defensive, but Jet says he's an outcast like himself and they need to have each other's back. Zuko states he's realized that being on one's own isn't always the best path.
Katara helps deliver the baby and they others go right in to see, except for Aang, but Katara tells him he has to see so he heads in. Amazed, Aang's expression changes from discouraged to encouraged. As the couple thinks of a name, Aang tears up and says "I've been going through a really hard time lately, but you've made me… hopeful again." The mother says she knows what they should name their daughter – Hope. The husband agrees.
Later Aang tells Katara he thought he was being strong, but he was really running away from his feelings. Seeing the family full of love reminded him of how he feels about Appa and about her. They embrace as the others walk toward them. Aang says he's going to try to find Appa and they wish him luck.
Suki tells Sokka she needs to get back to her warriors and Sokka is surprised to realize she came to protect him. Suki apologizes for the previous night, but Sokka stops her with a kiss.
Aang reaches the wall and majestically ascends to the top only to be shocked to see a huge mechanical drill with the Fire Nation emblem emblazoned upon it. Aang turns to Momo and says, "Sorry Momo, Appa is going to have to wait." The drill moves menacingly forward.