Each of the Gaang gets to pick a location for a mini-vacation. Katara's choice, the Misty Palms Oasis, is somewhat less cool than it was a hundred years ago, but they do meet a traveling historian, Professor Zei (Raphael Sbarge), who recognizes Aang as an Air Nomad. He (the scholar) is trying to find a legendary library out in the desert, one reportedly run by the great knowledge spirit Wan Shi Tong. Because of the extensive flying necessary to find it, and the less-than-solid nature of sand as a medium, Toph is essentially reduced to total blindness; she spends most of the episode in the shade of the building, trading good-natured grumbling with Appa.
Inside the Library, Wan Shi Tong allows them free run of the place, but only if they promise not to use any of his knowledge to hurt others. Sokka, unfortunately, comes across a scroll talking about "the darkest day in Fire Nation history," and becomes convinced that he has found a Weaksauce Weakness he and his friends can exploit. By utilizing the library's planetarium, he discovers the obvious pun behind the scroll: the "darkest day" of Fire Nation history was during a solar eclipse, when Firebenders lose the ability to bend. Of course, by now Wan Shi Tong has caught wind of what's going on, and he begins to submerge his Library beneath the sand for all eternity. Sokka, Katara, Aang and Momo flee, abandoning Professor Zei, who elects to stay and learn all he can.
Outside, Toph is having problems of her own. The local Sandbenders have arrived and are intent on capturing Appa. Blind, powerless, basically unable to do anything productive except fight against the (stone) Library's submerging, Toph is unable to prevent the Sandbenders from roping up the sky bison and dragging him away. At the mid-season cliffhanger, the Gaang are now stuck in the middle of a desert with no supplies or transportation.
- All Animals Are Dogs: The Fantastic Foxes beg for food and make sounds like dogs.
- Ancient Keeper: Wan Shi Tong, the owlish guardian of the ancient library.
- Badass Boast: Wan Shi Tong gets a good one when he's cornered Katara, boasting how he knows all kinds of Waterbending techniques.Wan Shi Tong: Your waterbending won't do much good here. I've studied Northern Water style, Southern Water style, even Foggy Swamp style!
- Bad Liar: SokkaWan Shi Tong: If you're going to lie to an all-knowing spirit being, you should at least put some effort into it.
- Great Big Library of Everything: The Library is legendary for its supply of books. Professor Zei says (as the library is withdrawing into the spirit world) that he could spend his life searching and never find a greater store of knowledge.
- Break the Haughty: Toph, a few episodes ago, boasted about being able to carry her own weight. Not until this episode does she realize she's pretty much helpless in a fight on sand. Just to rub it in, this results in her being unable to prevent Appa's kidnapping, whom Aang angrily said to Toph a few episodes ago that the bison carries everyone's weight - including hers.
- That library where Zhao learned about the Moon and Ocean Spirits' physical forms? It's Wan Shi Tong's.
- Katara is still carrying the waterbending scroll she "borrowed" from the pirates. She gives it to Wan Shi Tong.
- Collapsing Lair: The library.
- Continuity Creep: Season one was largely standalone episodes with a few minor ongoing plot threads. Season two introduced more continuity, until this episode begins a much tighter story arc that lasts the rest of the season.
- Did You Just Punch Out Cthulhu?: Sokka, of all people, gets this moment defending the Gaang from the berserk Owl Guardian.Sokka: That's called "Sokka Style." LEARN IT!
- Ditzy Genius: Professor Zei
- Downer Ending: The Gaang may have found out crucial info about the Fire Nation, but this is little consolation for the fact that they are in the middle of the desert with no supplies, no transportation, and no way to find the kidnapped Appa.
- Exorcist Head: Wan Shi Tong. Justified in that he's an owl.
- Fantastic Foxes: Wan Shi Tong's knowledge seekers. They are magical foxes who roam the world, seeking new books to add to his library.
- Forgot the Disability: Growing bored with the search for the Library, Toph suddenly shouts that she sees it, causing the rest of them to look in her direction excitingly, only to remember that she is blind.
- Gilligan Cut: When Katara wants to go to the misty palms oasis, Aang praises the place. Cut to the gaang arriving and finding the place dried out and deserted.
- Heh Heh, You Said "X": Aang and Sokka snicker when Professor Zei admires the library's buttresses.
- He Knows Too Much: Wan Shi Tong wants to kill the gaang because they already learned too many secrets from the library.
- I Choose to Stay: Despite it meaning certain death or at best, no way to return to the mortal world, Zei's love of knowledge is too great and he chooses to stay with the library as it goes under.
- Load-Bearing Hero: The only reason the Gaang even managed to escape Wan Shi Tong's library in time was because Toph was there to keep it from sinking too quickly.
- Mid-Season Twist: There will be a solar eclipse in a few months that will depower the Firebenders.
- Myth Arc: Continued in this episode. Sokka discovers records of "the darkest day in Fire Nation history," leading him to discover that a solar eclipse is due at the end of the summer.
- Nice Job Breaking It, Hero!: Sokka loudly proclaims "the Fire Nation's going down!", not knowing that Wan Shi-Tong happens to be right behind him. Rather than allowing his knowledge to once again be used to bring harm to others, the owl spirit decides to submerge the entire library permanently underground, and the Gaang just barely manages to escape.
- Ominous Latin Chanting: While Aang is looking at the lion turtle scroll.
- Ominous Owl: Wan Shi Tong switches, particularly when he finds out that the Gaang is planning on using the information they gained to invade the Fire Nation.
- One-Winged Angel: Wan Shi Tong initially looks like a regular owl when they meet him. But when he finds out what the group are doing, his form becomes much more larger and menacing.
- Redundant Researcher: Professor Zei.
- Sadistic Choice: Subverted. It looks like Toph has to choose between saving Appa from the sandbenders or stopping the library from sinking with the rest of the Gaang inside, but then you realize it's not really a "choice". She's blind in the sand, and her few attempts to attack the sandbenders are unaimed and don't hit anything. If she'd chosen to try to save Appa, she'd have failed, and the Gaang would've been buried with the library.
Professor Zei: The spirits spared no expense in designing this place.
- The scene where Wan Shi Tong pursues Katara around the library (including with her hiding behind a bookcase) is quite similar to the Velociraptor hunting the kids in the kitchen from Jurassic Park.
- The Sandbenders that appear are reminiscent of the Tusken Raiders.
- This quote from Professor Zei while climbing into the Library.
- Sunken City: Wan Shi Tong's library, fully covered in sand.
- Tap on the Head: Sokka disables the (not so) mighty Wan Shi Tong with his boomerang.
- Total Eclipse of the Plot: We learn that a solar eclipse is conveniently up in a few month.
- Unusual Euphemism: "I've been training my arrow off." (But since it's Aang, it's an innocent double entendre; what he means is that he's trained hard enough to wear off his arrow-shaped tattoo.)
- Voice of the Legion: Wan Shi Tong, the owl, speaks like this. And it is terrifying when he does so while going after the Gaang.