"It's the Fire Nation. They've closed in on the North Pole."
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.
- 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.
- 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 again.
- 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.
- 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.
- 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.
- 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.
- Nonindicative Name: Not technically a siege.
- One-Man Army: Averted. Despite being possibly the most powerful bender in the world, Aang can't single-handedly take on a whole navy.
- Phlebotinum Battery/Field Power Effect: "You rise with the moon. I rise with the sun."
- The Siege
- Snow Means Death: Black snow, to be precise.
- Stop Helping Me!: In-universe, so not subjective.
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!
- Take That: Confirmed by Word of God.
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?"
- Upper-Class Twit: Hahn is essentially the Northern Water Tribe's equivalent. 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.
- 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.