Plot

Aang, a young successor to a long line of Avatars, must master all four elements and stop the Fire Nation from enslaving the Water Tribes and the Earth Kingdom.

The world is divided into four kingdoms, each represented by the element they harness, and peace has lasted throughout the realms of Water, Air, Earth, and Fire under the supervision of the Avatar, a link to the spirit world and the only being capable of mastering the use of all four elements. When young Avatar Aang disappears, the Fire Nation launches an attack to eradicate all members of the Air Nomads to prevent interference in their future plans for world domination. 100 years pass and current Fire Lord Ozai continues to conquer and imprison anyone with elemental "bending" abilities in the Earth and Water Kingdoms, while siblings Katara and Sokka from a Southern Water Tribe find a mysterious boy trapped beneath the ice outside their village. Upon rescuing him, he reveals himself to be Aang, Avatar and last of the Air Nomads. Swearing to protect the Avatar, Katara and Sokka journey with him to the Northern Water Kingdom in his quest to master "Waterbending" and eventually fulfill his destiny of once again restoring peace to the world. But as they inch nearer to their goal, the group must evade Prince Zuko, the exiled son of Lord Ozai, Commander Zhao, the Fire Nation's military leader, and the tyrannical onslaught of the evil Fire Lord himself.—The Massie Twins

The four nations of Air, Water, Earth and Fire lived in harmony until the Fire Nation declared war. A century later, there is still no end in sight to the destruction, then, an Avatar named Aang (Noah Ringer) discovers that he has the power to control the four elements. He joins forces with Katara (Nicola Peltz), a Waterbender, and her brother, Sokka, to restore balance and harmony to their world.

A 100 years ago, all was right with the world. The four nations of Fire, Water, Earth and Air Nomads lived in harmony with each other. The Avatar was the only person who could control all the 4 elements in all the nations. He was also the only one who could communicate with the Spirit world and with their guidance, keep the balance in the world. Then suddenly, the Avatar disappeared. His disappearance allowed the Fire Nation to declare war on the other nations (the Air Nomads, the Water Tribes and the Earth Kingdom) in their attempt to conquer the world. A century has passed since then.

14-year-old Katara (Nicola Peltz) Southern Water Tribe and its last remaining Waterbender, and her 15-year-old warrior brother Sokka (Jackson Rathbone) are near a river at the South Pole. The Southern Water Tribe was once a great city, and their father is off fighting the war. Their mother was taken prisoner and killed when they were kids. Food is scarce and they often go hunting. They soon follow some tracks of a tiger seal. When they look beneath their feet, there was something glowing below and discover an unusual iceberg. Sokka hits the floor with his boomerang and a sphere of ice emerges from the water. Katara breaks into the sphere which releases a beam of light.

The ice sphere releases a boy named Aang (Noah Ringer) and a flying bison named Appa who were trapped inside. Unknown to them, Aang is the long-lost Avatar - a spiritual figure that holds the world in balance through every incarnation.

Katara and Sokka bring Aang to their village. Aang says that he ran away from home as he was upset. But then he was caught in a storm and forced under the water of the ocean. He thanks Katara for rescuing him and Appa.

Zuko (Dev Patel), an exiled prince of the Fire Nation, is on a quest to find the Avatar and bring him as prisoner to his father, the Fire Lord Ozai (Cliff Curtis). Seeing the light that appeared from Aang's release, Zuko and some Fire Nation soldiers arrive at the Southern Water Tribe to demand the villagers to bring out their elderly under the impression that the Avatar must be an old person. But Aang reveals himself as he surrenders himself to Zuko on the condition that he agrees to leave the village alone.

Katara's aunt tells her Aang is the missing Avatar (as she had looked at his tattoos) that the Avatar's destiny is to bring peace to the world & that Katara and Sokka need to help him. Aunt says that only the Avatar can speak to the spirits of the Spirit World, who seek to maintain balance. It is filled with the most amazing forms of dazzling creatures that exist in the most exotic valleys, mountains and forests. The spirits have watched over the world since the beginning. The Fire Nation doesn't want to live by the Spirits, which is why the Avatar frightens them. They realize that Appa can float.

On the ship Aang is tested by Zuko's Uncle Iroh (Shaun Toub) to confirm him to be the Avatar. After being informed that he is to be their prisoner for passing the test, Aang escapes using his glider and flies to his flying bison brought by Katara and Sokka. Aang and his new friends visit the Southern Air Temple, and he learns that he was in the ice for a whole century and that the Fire Nation wiped out all Air Nomads as they knew that the next Avatar would be born into the Air Nomads, including his guardian, Monk Gyatso (Damon Gupton). In despair, he enters the Avatar state and finds himself in the spirit world where he encounters a dragon spirit that tells him to make his way to the Northern Water Tribe to master Water Bending. Katara's pleas bring Aang out of the Avatar State.

While at small Earth Kingdom town controlled by the Fire Nation, Aang's group is arrested because Katara tries to help a young boy (Isaac Jin Solstein) from a patrol. They incite a rebellion by reminding the disgruntled Earthbenders that earth was given to them.

The rescued tribe gives Katara Waterbending scroll that was stolen by the Fire people from the water bending tribes, which she uses to perfect her Waterbending and help Aang learn Waterbending as they make their way to the Northern Water Tribe and liberate more Earth Kingdom villages in the process. Aang had revealed to Katara that he had run away before the monks had completely trained him to be an Avatar & hence needed to be taught how to bend Earth, Fire and Water. Aang says that he ran away because the monks told him that as an Avatar, he could not have a normal life or a family. They make their way to the Northern Water Tribe where Aang can learn from water-bending masters.

During a sidetrack to the Northern Air Temple on his own, Aang is betrayed by a peasant and captured by a group of Fire Nation archers, led by Admiral Zhao. Zhao hates Zuko and covets the throne. Zhao was following the trail of liberated villages that Aang was leaving behind in his wake. Zhao also tells Emperor Ozai that he has captured a library of scrolls which indicate where the ocean spirits live in this world. If the spirits are killed, the Northern tribe & all its water benders will lose their Waterbending abilities. Ozai warns Zhao to capture the Avatar before Zuko. If Zuko captures the Avatar, he will return a hero, take the throne & become Zhao's boss. Ozai had banished Zuko when Zuko stood up to a General who wanted to sacrifice Zuko's friend in a senseless battle. Ozai punished Zuko by challenging him to a fight & when Zuko refused to fight his father, Ozai declared him soft & banished him.

In captivity, Aang again visits the spirit world where the dragon spirit tells Aang that Zhao has stolen the scrolls which reveal the location of the of ocean spirit, whom they plan to kill. If so, the water benders will lose powers & Northern Water tribe will fall. He instructs Aang to protect the Northern water tribe. However, a masked marauder, the "Blue Spirit", helps Aang escape from his imprisonment. Aware that Zuko is the "Blue Spirit", Zhao arranges to kill the prince. Zuko survives the attempt on his life. Zhao has a crossbowman fire a bolt that knocks Zuko out, but Aang uses his skills to escape with the unconscious Zuko. Aang watches over Zuko until morning, then leaves to reunite with Sokka and Katara. Zhao tries again to kill Zuko by blowing up his ship, but Zuko secretly survives.

With Iroh's help, he sneaks aboard Zhao's lead ship as his fleet departs for the Northern Water Tribe to execute the plan, he and Ozai set up with the scrolls from the Library detailing the spirits there. They want to prevent the Avatar from learning water bending & defeat the Northern Water tribe by killing the Moon & Ocean spirit, whose location the scrolls reveal to be near the Northern tribe itself.

Upon arriving, Aang's group is welcomed warmly by the citizens of the Northern Water Tribe. Immediately, Sokka befriends the Northern Water Tribe princess, Yue (Seychelle Gabriel). After a few agreements, a Waterbending master, Pakku (Francis Guinan), teaches Aang Waterbending. Soon, the Fire Nation arrives, and Zhao begins his attack while Zuko begins his search for the Avatar on his own by entering the city by stealth & tracking Aang to a sacred temple &, capturing Aang as he enters the spirit world to find the dragon spirit to give him the wisdom to defeat the Fire Nation. The Dragon Spirit advises him to "use the ocean and show the power of water".

Returning to his body, Aang battles Zuko before Katara freezes him. Meanwhile, at the city gates, Zhao orders the attack on the Northern tribe, Iroh watches Zhao capture the Moon spirit Tui, which with its water spirit counterpart had assumed the form of a fish. Despite Iroh's pleas, Zhao kills Tui to strip the Waterbenders to lose all of their powers and abilities to Waterbend. Iroh has had to fake accepting Zhao's invitation to join his fleet as a general (after faking Zuko's death) & does not agree with Zhao's plan to kill the Moon spirit as he has too much respect for them. Enraged by Zhao's sacrilege, Iroh reveals his mastery of fire-bending, frightening Zhao and his entourage out of the sacred cave.

Yue explains to everyone that the Moon spirit gave her life, & that she is willing to give it back to bring the Moon and Ocean spirit back to life. With the tables turned, Zhao is drowned by Waterbenders after Zuko and Iroh leave him to his fate.

Recalling his life before being trapped in the ice, Aang enters the Avatar State and raises the ocean into a gigantic wall to drive the Fire Nation back. Aang now fully embraces his destiny as the Avatar as he, Katara and Sokka prepare to continue their journey to the Earth Kingdom to find an Earthbending teacher for Aang. When news of Zhao's death and Iroh's betrayal reaches Fire Lord Ozai, he appoints his daughter Azula to capture both her uncle and Zuko along with dealing with the Avatar before Sozin's Comet returns.