"You wish to speak to Avatar Roku. I can take you to him."
Having being given a message from Roku's dragon in the Spirit World, Aang knows he must find the temple dedicated to Avatar Roku in order to contact him for advice before the solstice is over; however, said temple is within the Fire Nation. As he, Sokka and Katara attempt to infiltrate enemy lands, Zuko is hot on their trail- even though it means returning to his home country, where he is forbidden to go.
At the edge of Fire Nation waters, both sides discover a Naval Blockade
of Fire Navy warships, headed by Zhao. Pressed for time, Aang has Appa run the blockade
, with Zuko following suit. Though the Gaang makes it past, it looks like Zuko will be caught by Zhao- but instead, the Fire Nation commander decides to let Zuko past, so that he will lead him to the Avatar.
At the temple Roku's dragon showed Aang, the trio meet the Fire Sages of the Avatar- who attack! One sage helps the Gaang escape, revealing that he only is still loyal to the Avatar. The rest, during Aang's hundred-year absence, defected to the Fire Lord. Shyu, the sage, takes the three to a room where the statue of Avatar Roku is kept. But the doors are locked- only a fully realized Avatar or the five Fire Sages can open the firebending-controlled doors. Sokka tries to use explosives, but all it does is create scorch marks. This gives Katara an idea. The other sages show up, and Shyu declares that Aang has gotten into the statue room, and they open the doors to reveal it's actually Momo. Before Aang can enter the statue room, Zuko arrives to capture him. After a skirmish, Aang gets into the room just as the doors close. Attempts by Zuko and the other Fire Sages to force open the doors fail- Avatar Roku wants a private audience with Aang. Then Zhao shows up to arrest both Aang and Zuko.
Aang stares at the statue of Roku just as light from the Winter Solstice hits the jewel on its forehead. The eyes glow, and Aang is now standing with his past self- Avatar Roku. Aang's past life explains that the comet Aang saw in his vision last episode was used by Fire Lord Sozin to start the war; the heat from it gave all firebenders extra power. The comet will return by the end of Summer, and Fire Lord Ozai will use it to end the war. Aang must
master all four elements and defeat the Fire Lord before that can happen! With the solstice ending, and sensing great danger in the temple, Roku offers to give Aang some extra help...
In the temple, the doors to the statue open- but instead of Aang, Zhao and the Fire Sages meet Avatar Roku. The past Avatar unleashes his power on the disloyal sages, and sets off a chain reaction that starts to destroy the temple. The Gaang and Zuko manage to escape in the chaos, much to Zhao's fury.
- Comet of Doom: Roku summoned Aang to the Fire Temple so that he could warn Aang about Sozin's Comet. This quickly came under questioning from older fans as comets are made of ice, dirt, and gas — that is, every element except fire — before it was clarified that the comet has supernatural properties (as comets in our world were once rumored to have) that simply strengthen Firebenders, as opposed to the Fire Nation bending the comet itself, like a missile.
- Comets aren't that punctual either, and normally stay in the sky for weeks. Hence, this is a earth-grazing fireball that the characters call a comet.
- The series finale answers both questions. The comet briefly grazes the atmosphere, greatly warming the earth and thus providing more warmth for the firebenders to use.
- Convection Schmonvection: the notorious first example in the show of characters just strolling through magma-filled secret passageways without breaking a sweat. Two characters are Firebenders (or, at least, one is a potential Firebender). The others have no excuse.
- Idea Bulb: Sokka gets an idea and the camera pulls back to reveal a lamp above his head.
- Mid-Season Twist: The series jumps from "Let's take Katara to learn Waterbending" to "kill Ozai in a year or the world gets destroyed".
- Naval Blockade: The Gaang has to get to a temple inside the Fire Nation, the border of which is blockaded by the Fire Navy.
- Old Master: The first time we see what an Avatar can do with firebending.
- Ominous Latin Chanting: Shortly before the sanctuary doors open to reveal Avatar Roku.
- Running The Blockade: Aang pulls Appa into a steep dive to build speed and then rushes past the Fire Navy, dodging fireballs the whole way. Zuko, following Aang wherever he goes, is about to perform a more traditional run, but Zhou decides to let him through and follow after.
- Wham Episode: Aang has to defeat Ozai before Sozin's comet returns in midsummer, or else Ozai will be unstoppable...