*Finale Spoilers below*

- 1 episode finding Ursa

- 1 episode dealing with Azula in prison

- 1 episode dealing with a Fire Nation prison in which the gaurds remain loyal to Ozai and try to kill off its prisoners before they are released, and Aang plays a crucial part in stopping them.

- 1 episode dealing with a political assassin trying to take Zuko's life

- 1 episode dealing with a vengeful group of vigilantes trying to kill ex-FN generals and soldiers

- 1 or perhaps several episodes dealing with the FN civillians question the power and good of Zuko, still believing Ozai's propaganda and they have to be convinced otherwise

- 1 or 2 episodes concerning Aang teaching a non-bender air bending forms and tecniques so that, even though he's a non-bender, he can aid in preserving the art of airbending even if he never manages to have air nation kids to teach. Or he could teach Katara the moves; that'd be good to.

- 1 episode concerning a terrorist group of Ozai loyalists

- 1 episode concerning the recovery of Air temple relics, perhaps with flashbacks to life at the air temples

- 1 episode concerning helping some refugees find loved ones or a specific loved one

- 1 episode concerning the earth king and bringing him back to Ba Seng Sei

- 1 general aftermath episode concerning everything from homeless people who no longer have families to cities who no longer have leaders after being Fire Nation for so long but no more to general physical rebuilding

- 1 concerning the rebuilding of the Southern Water tribe

- 1 concerning an Earth Kingdom city in which any Fire Nation citizen who entered would be arrested and thrown in jail

- 1 Fire Nation colony who refuses to release its grip on an earth kingdom town, standing against the ending of the war

- Finale episodes concerning an evil FNl general, perhaps one from the previously mentioned prison episode, and his plot to break out Ozai and Azula and overthrow Zuko much like the Dai Li planned to do after Long Feng was arrested.

There's definitely enough material for a book 4 Air

ehhh if I wrote it

Zuko would break Azula out of Jail to look for their mother, and there would definatley be some Zutara , im not a zutara fan but It would be cool if they had just kissed or something, just not end up together

Maybe Aang could find out that there's actually another Airbender in the world besides him and go's to look for him/her

Personally I believe Avatar is BEGGING for a fourth book. Besides it being a hit show with a loyal fan base, it also has many loose ends and plot hooks to make a very interesting season. Teranef summed up much of the leftover material; of itself, it would be enough for a couple of good "aftermath" episodes (finding Ursa and confronting her with Azula as the #1 plot), and fine background filler for the rest. However, it just doesn't stand up on its own as the backbone of an entire season.

No, considering what has been done in Books 1-3, and the power achieved by the characters, Book 4 would have to be really spectacular, but go off in a new way (i.e. no crazed firebenders as main villains).

Here's what we have by the end of Book 3 (and seriously, if you haven't already seen the finale, what are you doing here?):

1. Aang can enter Avatar State at will;

2. Trans-national order of the Masters, which might as well include Zuko, Katara & Toph;

3. Fire Nation defeated, their greatest generals/benders either dead, imprisoned, or defected;

4. Spirit-bending.

I think that for Book 4, Spirit bending would have been a great central theme. We have only seen a glimpse of it, but it's obviously immensely powerful and able to subvert even the most powerful bender by strength of will. We know it can take away bending skill/talent, but judging from the name, it could also be conceived to do a variety of other things, such as: returning the bending that was taken away; granting powers to people previously devoid of them; or even mental domination (think bloodbending on a mental level).

A great foil to the mighty gAang would have been someone able to use Spirit bending for evil purposes.

As this art has been forgotten ever since the first Avatar, only the spirits probably have any knowledge of it.

Of all spirits, the most sinister was Koh; he's also said to be one of the most ancient, possibly predating the Avatars. Sure, he didn't use any Spirit bending on Aang; but then again, bending doesn't work in the Spirit world, so to use it, he'd have to incarnate in the material world.

Koh is also powerful in his own right ??? he's probably a shapeshifter, able to turn into anyone whose face he stole. He's also probably more evil than Ozai ??? a creature of pure darkness and malice, ever hungry for fresh souls (or bodies?) to feed his appetite, yet intelligent enough to conceive a plot that would harm the world more than Ozai's plan ??? perhaps, to turn all humans into vicious predators under his control, consume their spirit energy, and set up himself as the new God/Avatar.

Combined, Spirit-bending and shapeshifting would create a very powerful opponent who could easily play to the weaknesses of the gAang ??? they are very strong in terms of brute force, but lack any sort of clairvoyance to track a stealthy, shapeshifting villain who uses mental domination to corrupt innocents into evil thralls. He could also free Ozai & Azula, and with the Fire Lord's bending back, these two would make great lieutenants / secondary villains, rallying some of the Fire Nation army. It would also add tension to Azula's character, who at that point might have been visited by Ursa, Zuko, Mai and Ty Lee, and would arrive at similar crossroads as Zuko in seasons 2-3. And it would give some angst to Aang, who would consider whether they were right to let Fire Nation evildoers live, now that the criminals have escaped and are at large again, as well as what to do with the new unknown menace.

Go Book 4: Spirit!