In the Northern Water Tribe, things are going great for our heroes. Aang and Katara are advancing quickly in their water bending lessons, and Sokka's friendship with Yue grows, even though he knows he can't have more. That all changes when they discover the Fire Nation Navy advancing with hundreds of ships.
With no other choice, the Water Tribe is forced to go to war; Aang attempts to attack the ships head on, while Sokka volunteers for a guerrilla mission, facing both death and Yue's jerk fiance Hahn. In the Fire Nation camp, Zuko hides in a disguise, before going solo into the Water Tribe in an attempt to kidnap Aang. Zhao, meanwhile, alludes to a secret plan of his own: to kill the Moon Spirit, the source of all Waterbending.
The reason Zhao can do this at the North Pole is that here, in the Spirit Oasis, the Northern Water Tribe's inner sanctum, live Tui and La, the spirits of the Moon and Ocean respectively. They inhabit the bodies of two koi, circling endlessly in the oasis' pool. Aang, his battle against the fleet fruitless, comes here to meditate, hoping to bring the spirits in on his side; Katara stays to defend him while Sokka and Yue oversee the defenses. It is here that Zuko finds him, and though Katara puts up one hell of a defense, Zuko defeats her and kidnaps Aang. This has the side effect of stranding Aang in the Spirit World, as his body is not where he left it. The episode ends with the walls of the city breached and Zuko toting Aang across the frozen tundra.
- Accidental Misnaming: Hahn can't get anyone's names right.
- Alertness Blink: When Aang is destroying the Fire Nation ship's catapults, he is surprised by a soldier, causing two white flashes next to him and a clear blinking sound.
- Answer Cut: When Arnook says "It is with great sadness I call my family here before me, knowing well that some of these faces are about to vanish from our tribe," the camera flashes to Yue, Pakku, and Hahn.
- Attack! Attack! Attack!: Averted, or perhaps subverted considering the character in question. Zhao sees the merit in Iroh's advice not to rush in and begin battle with the looming emergence of the moon, from which the waterbenders can draw greater power; he instead anchors his navy while ironing out a plan to deal with the problem.
- The Bad Guy Wins: Sort of. After being put through a lot of crap, Zuko finally captures the Avatar and escapes. Though, we know in the next episode, he loses again.
- Badass Boast: See Take That! and keep in mind that this show is the only show to beat out Spongebob Squarepants at the Kids Choice Awards.
- Big Damn Heroes: Once again, Appa saves the day.
- Braving the Blizzard: Zuko captures and takes Aang (who is in the Spirit World) further up north to avoid Zhao and his forces. It goes poorly because the North Pole is barren for miles and ends up encountering a violent blizzard.
- Call-Back: Some of the waterbenders stop a Fire Nation ship like the one seen in "The Boy in the Iceberg".
- City of Canals: The Northern Water Tribe's city.
- Curb-Stomp Battle: At night under the full moon, Katara thumps Zuko repeatedly with her improved training and special tide-induced boosts. But then the sun rises, and Zuko's power boosts activate, letting him burn through all ice attacks and knock Katara out with one blow. They have a third battle later after finding Aang, where Katara curb stomps him again. Lampshaded by Katara just before the third battle.Katara: I don't think it will be much of a battle. (Cue curb stomp)
- Dual Wielding: While sabotaging the Fire Nation ships, Aang gets attacked by a soldier wielding two hammers attached by chains.
- Flight of Romance: Sokka takes Yue on one. The Fire Nation ruins it.
- Instant Armor: Aang does this with snow as a joke.
- Jaw Drop: Sokka's reaction when he learns that Hahn is Yue's fiancé.
- Jerkass: Hahn. He tells right to Sokka's face that's pursuing Yue merely for the perks of being the chieftain's son-in-law.
- Like A Son Tome:Iroh: I just nag you because, well, ever since I lost my son...
Zuko: Uncle, you don't have to say it.
Iroh: I think of you as my own.
- Meaningful Name: 'Yue' is Chinese for 'moon', which fits how the moon spirit gave energy to save her life as a baby. It becomes all the more fitting when she literally becomes the moon.
- The Native Rival: Hahn, to Sokka. With a nice little subversive twist, in that Sokka is a rustic tribesman from a backwater village in an urban setting.
- Noisy Nature: Zuko finds some sealion-turtles that won't stop making noise while infiltrating the North Pole, and yells at them to be quiet.
- Non-Indicative Name: Not technically a siege.
- Oh, Crap!: Aang's reaction when, after subduing the first Fire Nation ship, he sees that there are still hundreds on their way.
- One-Man Army: Averted. Despite being possibly the most powerful bender in the world, Aang can't single-handedly take on a whole navy.
- Opening Shout-Out: When Aang decides to actively fight against the Fire Nation invasion, there is a shot of him from behind holding his staff, followed by a pan up into the sky, which is identical to that at the end of the opening sequence.
- Phlebotinum Battery: "You rise with the moon. I rise with the sun."
- Punishment Detail: Subverted. Sokka expected Arnook to possibly sentence him to some grim punishment such as scrubbing the barracks for his insubordination against Hahn, but no, he needed him to guard his daughter.
- Reality Ensues: The Northern Water Tribe has been in near total isolation for almost a century so when they pull out "Real" Fire Navy uniforms for an infiltration mission the captured uniforms are totally out of date because no one has seen a fire nation solider for decades.
- Snow Means Death: Black snow, to be precise.
- Take That!: Confirmed by Word of God.Pakku: A couple years and you might be ready to fight a sea sponge.
- Took a Level in Badass: Katara's fighting skill was already good enough to give Master Pakku a decent workout in the previous episode. Within a very short time, Katara's at the top of the class pummeling all the other trainees in under 30 seconds.
- Zuko even acknowledges it with a complimentary insult: "You little peasant, you found a master haven't you?"
- Unwanted Assistance: Understandably, Yue is undoubtedly unaware of how the Avatar's power works, which leads her to think something is wrong with him.Katara: He's meditating. Trying to cross over into the Spirit World. It takes all his concentration.Yue: Is there any way we can help?Aang: How about some quiet?! Come on, guys, I can hear every word you're saying!
- Upper-Class Twit: Hahn is essentially the Northern Water Tribe's equivalent, due to warriors being one of the most respected classes. He even insults Sokka based on the fact that he's from the Southern Water Tribe, and states that he "wouldn't understand the political complexities of our tribe". Said political complexity is Hahn wanting to marry Yue for the perks. He also gets annoyed when Sokka points out the stolen Fire Nation armour is several decades out of date, and can't get Zhao's name right at all.
- We ARE Struggling Together: Sokka ends up getting into conflict with Hahn, as the former knows Zhao and the Fire Nation a lot better than he does, and calls him out for being a self-absorbed jerk, while Hahn insults Sokka for his ignorance of his tribe's political complexities. The chieftain would have none of this infighting amongst his ranks that he had to take Sokka off the mission.
- Worf Had the Flu: Played both ways; both times Katara beat Zuko she had the moon on her side and he had trudged through the arctic (which would weaken anyone but especially firebenders). The one time he beat her, he had the sun and also managed to get her from behind with a lucky shot.