Shiro Shinobi: [Narrating a newsreel.] After ten thousand years, Harmonic Convergence is here again, and the dark spirit Vaatu is free. Tenzin, Bumi, and Kya have entered the portal to rescue Jinora's spirit. Asami split from the group and took the injured Tonraq to safety. So it's up to Korra, Mako, and Bolin to stop Unalaq before he fuses with Vaatu and becomes a Dark Avatar.

[Shot of the back of Vaatu hovering above the Tree of Time looking down at Korra, Mako, and Bolin. Cut to close-up of Unalaq looking up at Vaatu in amazement. Unalaq turns to the Avatar and the two brothers, who are standing behind him.]

Vaatu: [Frontal of Korra with Mako and Bolin in the background. Addressing the light spirit within Korra.] Raava, [Shot changes to show the back of Korra and front of Vaatu.] nothing could stop this moment. Harmonic Convergence is upon us again.

Korra: [Aerial frontal.] I'm not going to let you fuse with Unalaq. You're going right back in that prison.

[Vaatu tries to fuse with Unalaq as Korra enters the Avatar State and stops him with a large blast of fire. She catches Unalaq with airbending, lifting him off the ground, and flings him back through the portal.]

Korra: [Shot of Korra out of the Avatar State and turned to Mako and Bolin.] Don't let Unalaq back in the Spirit World.

Bolin: [Close-up of the two brothers.] We're on it.

[Mako and Bolin run through the portal, and Korra turns back to Vaatu, who is charging right at her. Korra reenters the Avatar State and charges at Vaatu via a thrust of firebending. Cut to Tenzin, Kya and Bumi walking through the Spirit World.]

Bumi: Jinora. Jinora's spirit do you hear me? [Frontal of all three.] It's your Uncle Bumi.

Tenzin: [Bumi turns to Tenzin.] Ah, this isn't working. We can't just randomly wander the Spirit World, call out for Jinora, and expect to find her.

Bumi: We just need to employ the simply rules of tracking. [Cut to Bumi kneeling down.] First we locate her footprints ... then we follow them.

Kya: [Frontal of Kya and Tenzin.] Do you even know what spirit footprints look like? Do spirits even leave footprints? Face it, your tracking skills won't work in the Spirit World. [Sits down on the ground in a meditation position.] Let me try something. [Close-up of Kya performing mantra meditating.] Jinora is over there. [Close-up stops.] I feel a lot of spiritual energy coming from that direction.

Bumi: We're in the Spirit World. There's spiritual energy in every direction.
Tenzin: Enough! [Frontal of Tenzin.] We can't do this by ourselves. We need a spirit guide.

[Tenzin walks away followed by Kya and Bumi. They approach a hole in the trunk of a large tree with a glowing star inside.]

Tenzin: [Side shot of all three before the tree.] There. [Cut to shot looking into the hole showing the backs of Tenzin, Bumi, and Kya.] Spirit, hello. [Close-up side shot.] I'm sorry to disturb you, but I am in need of your assistance.

Dark Spider Spirit: [Shot inside the hole.] You dare wake me, human? Humans in the Spirit World belong in one place only.

[The spirit emerges from the hole and charges at the three humans. Shot from the spirits perspective. Bumi and Kya run away, followed by Tenzin; frontal shot of the spirit chasing them. Cut to the three at the edge of a cliff as they jump off and land below, dazed. Close-up of the group as Tenzin airbends everyone to their feet.]

Bumi: [Brushing off dust.] Well, that didn't work. Now where are we?

Tenzin: We're completely lost.

[Cut back to the portals where Korra is using all four elements to launch several attacks at Vaatu, only to have Vaatu dodge them. Korra enters the Avatar State and charges at Vaatu, and using airbending and firebending, destroying parts of his essence in the process. Korra propels herself over the ground with firebending, while Vaatu attacks her with his tendrils. She breaks his hold on her and charges at him with firebending, obliterating a large portion of him. Vaatu turns back to Korra and knocks her off before slamming her against a rock with his energy beam. He ensnares Korra with vines, incapacitating her.]

Korra: No!

[Cut to the South Pole where Mako and Bolin are in vigil and in fighting stance. Cut to a far shot of the brothers, followed by an unknown portion of the forest where a mysterious assailant attacks them with rapid ice spikes. Mako gasps while his brother protects him with an earth wall. Mako firebends from behind the wall, while Bolin earthbends in the direction of the assault. Cut to the brothers who look on in silence, before they were interrupted with a barrage ice spikes from the opposite direction. The brothers manage to dodge the attack by separating. Mako attacks with firebending, while Bolin somersaults while earthbending. When he bends another rock, he is struck by an ice spike. The rock managed to protect him, but the impact threw him toward Mako.]

Bolin: I don't know if we can win this fight.

Mako: We don't need to win, we just need to stop Unalaq from getting back in the Spirit World.

[The brothers are attacked with another barrage of ice spikes, but Bolin stops the attacks with an earth wall.
Cut to the Spirit World where Tenzin, Kya and Bumi wander about a mysterious spirit forest, completely lost. When they walk past a spirit mushroom, Tenzin turns are look at it.]
Tenzin: [Close-up.] We're walking in circles, [Pointing at the mushroom.] I've seen that same spirit mushroom five times.

Bumi: That's not the same mushroom.

Spirit mushroom: Yes I am.

Tenzin: See? Even it knows we're lost. [Facepalms.]

Bumi: [Annoyed.] Oh sure, listen to a fungus over your own brother.

Kya: [Walks up to her brothers; suspiciously.] What's that?

Bumi: Mushroom? Is that you?

Spirit mushroom: No, wasn't me.

[A figure approaches the siblings, causing them to gasp in fear and caution. Cut to the mysterious figure, who turns out to be Iroh and a knowledge seeker.]

Bumi: Iroh?!

Tenzin: How ...? Where ...? It's been so long.

Iroh: Almost forty years. It's nice to see you again.

Tenzin: How did you know we were here?
Iroh: [Stroking the spirit.] My friendly spirit fox told me you were lost, I came to show you the way out.

Tenzin: Iroh, we are grateful, but we're not looking for the way out. We're looking for my daughter.

Iroh: I'm sorry to hear that. But you shouldn't be here, Vaatu has escaped and darkness threatens to take over.

Tenzin: I'm not leaving until I find Jinora.

Iroh: I understand. But I beg you to be careful, if you travel too deep into the Spirit World, you could end up in a place where only the lost will ever find you.

[The siblings look at each other in confusion. As they turn back, they noticed that Iroh had disappeared. Tenzin tries to catch up, but stops and contemplates.]

Tenzin: A place where only the lost can find you ...? That's it! I know where to find Jinora!

[Cut back to the portals where Korra struggles with the vines. She takes a deep breath and enters the Avatar State, breathing a large breath of fire at Vaatu. She frees herself by breathing fire at the vines before resuming the battle, where she attacks Vaatu with air, water and fire, before knocking him with two earth columns and a water blast. Korra approaches Vaatu on an air spout before trapping him in an air bubble, a ring of water, fire and earth, similar to what Avatar Wan did 10,000 years ago.]

Korra: [With the voice of her past lives and Raava's.] I'm locking you away for another ten thousand years, Vaatu!

[Korra prepares bringing Vaatu into the tree.
Cut to the South Pole, where Mako and Bolin are kept in vigil, with two earth walls to protect them.]

Bolin: Unalaq? [Peering over the rock.] Are you out there? [To Mako.] He must've gone home?

[As Bolin peers over the rock, his ex-girlfriend peers over from the other side.]

Eska: Hello, my feeble turtle duck.

[Bolin is shocked at his discovery before Eska knocks him off with waterbending. Mako turns to look at Bolin but Desna emerges behind him. Before he could retaliate, Desna knocks him off with waterbending toward Bolin. When the brothers have recovered, a large water blast knocks them off, unconscious.]

Unalaq: [Riding a wave.] Don't let them escape this time.

[Unalaq walks into the portal, with his children looking at each other with unsure looks.
Cut back to the Spirit World, where Tenzin, Kya and Bumi are standing outside the hollow of the tree where the dark spider scorpion spirit resides.]

Bumi: Are you this is the best way to find Jinora?

Tenzin: Trust me. [Attacks the spirit with an air blast.] Hey you! Spirit! Wake up!

Dark Spider Spirit: You again?!

[The spirit emerges from the tree, attacking the trio. Cut to the trio who were captured by the spirit in a web. Cut to a far shot of the large spirit dragging them to an unknown location. The spirit soon stops and swings her prisoners for them to look at a place. Cut to a far shot of the place, which is a canyon with sharp rocks. The view of the inside of the canyon is obscured by a thick fog.]

Kya: I thought we were gonna be taken to a prison?

Tenzin: This is a prison.

Dark Spider Spirit: Welcome to the Fog of Lost Souls. You will never escape.

[As the spirit walks away, it throws the trio into the canyon, who scream in the process.
Cut back to the portals, where Korra is nearly successful in locking Vaatu into the tree. As the ball glows, Korra is attacked by a water blast, allowing Vaatu to break free. Korra looks on to see Unalaq preparing another water stream, which knocks her out.
Cut back to the South Pole where Eska and Desna are dragging Mako and Bolin away. Unknown to the twins, the brothers soon regain consciousness and look at each other before nodding in agreement. Mako kicks a blast of fire at Desna to free himself, before throwing another blast at Bolin and Eska, separating them. Bolin run toward his brother, earthbending two earth columns to knock down Desna and Eska. The brothers run into the portal, where they see a free Vaatu and an unconscious Korra. Desna and Eska run through the portal.]

Eska: Stop!

[Eska bends out two streams of water and traps Mako and Bolin in ice blocks. Korra stands up to see Vaatu approaching Unalaq. Mustering as much strength as possible, she throws a fire blast, which Unalaq blocks with a blast of water. Vaatu flies over and enters Unalaq, who stumbles before standing erect again, with the imprint of Vaatu on his chest, and his eyes glowing orange-red. Unalaq approaches the Northern portal and touches it. The overlapping portals energize, engulfing Unalaq with purple energy, who lets out a blast of dark energy from his mouth. A blinding light shines from his body.]

Korra: No!

[As the energy dissipates, Unalaq opens his eyes, which glow orange-red, creating the Dark Avatar.]

Unalaq: We are now one! Now a new era for spirits and humans will begin! And I will lead them all as the new Avatar!

Korra: [Walking forward.] Well I'm the old Avatar, and my era's not over yet!

[A spout of air emerges behind Korra, and the two Avatars charge toward each other. As they attack, the scene changes to Bumi, Kya and Tenzin in the Fog of Lost Souls, where they wander aimlessly.]

Bumi: What kind of prison doesn't have any bars or walls? We can walk right out of here.

Tenzin: The Fog of Lost Souls is a spirit prison for humans. I read about that in ancient text. The fog is actually a spirit [Kya gasps and looks around cautiously.] that infects your mind and slowly drives you mad, imprisoning you in your own darkest memories.

Kya: [Turns to Tenzin with an uneasy look.] How long can we be trapped in here? [As Kya asks, Zhao walks by them.]

Zhao: I am Zhao, the Conqueror. [Tenzin's and Kya's eyes widen in surprise and turn to see Zhao.] I am the Moon Slayer. I will capture the Avatar. [Pause.] I am Zhao the Conqueror. [Kya's eyes widen in shock. Cut to a side shot of Zhao.] I am the Moon Slayer. I will capture the Avatar.

Kya: Hopefully we're not trapped in here as long as that guy.

Zhao: You, you're him. The last airbender! [Grabs Tenzin.]

Tenzin: [Terrified.] Ah, no! Get off me! [Zhao drags Tenzin toward him. Side shot of Zhao holding Tenzin.]

Zhao: You've grown. But I will still defeat you. [Kya and Bumi drag Zhao away with Tenzin staring at him in horror, Kya and Bumi push him away with Kya waterbending, the group ran away hastily and fearfully.] Come back Avatar. Face me! I am Zhao the Conqueror. I will capture you! Victory will be mine!

[Zhao fades into the fog. Cut to the group's waists being tied together by Tenzin with a rope.]

Tenzin: If we stay together, we'll find Jinora and make it out of this fog.

[Cut back to the South Pole, where the two Avatars emerge, with Unalaq chasing Korra. Korra attacks with firebending, which Unalaq neutralizes with large ice walls. Both make their way out of the encampment. Korra attacks Unalaq with airbending, but misses. Unalaq attacks Korra with ice shards, which Korra blocks before gaining altitude and assaulting Unalaq with large rocks. Unalaq breaks the rocks with two water whips and direct them toward Korra. Korra stops the whips with a large ice disc, but Unalaq throws her off toward the ground. Unalaq exits his waterspout and traps Korra in a fissure before closing it.]

Unalaq: Give in. Your time is over!

[Korra attempts to struggle free, but she soon weakens and faints. As she nearly passes out, the light spirit inside her begins calling her out.]

Raava: Korra, this fight is not over.

Korra: Raava.

Raava: Vaatu cannot win. Do not give in to ten thousand years of darkness. You are the Avatar.

[Korra's eyes light up. Cut to the surface, where fire erupts from the fissure, knocking Unalaq off. Korra emerges from the fissure via an air spout with a golden glow around her.]

Korra: You cannot win.

[Korra attacks Unalaq with an air blast, who dodges it by rising from a waterspout. He retaliates with a water blast, but misses.
Cut back to the Fog of Lost Souls.]

Tenzin: Jinora! Jinora!

Bumi: Wait a second.

Tenzin: What, do you hear something?

Bumi: [Stares around in morbid fear.] Yes. They're all around us. The cannibals, they're everywhere.

Tenzin: Bumi, you must focus your mind. Right now! There are no cannibals. [Kya looks suspiciously at herself.]

Bumi: Yes, there are! They're gonna eat every last one of us!

Kya: [Screams, startling her younger brother.] Who are you two? [Prepares to untie herself.]

Tenzin: [Stops his sister.] Kya, we're your brothers. You must remember, before the fog infects you.

Kya: No, you're just a vision. I have no family. You can't tie me down.

Bumi: They're closing in! I gotta get out of here!

[Bumi unties himself and runs away, screaming. As Tenzin tries to catch up, his sister unties herself and runs in the other direction, screaming before disappearing in the fog.]

Tenzin: No! Bumi! Kya! Come back!

[Tenzin airbends the fog away at both directions. As the fog returns, he doubles his power to dissipate the fog, but it still returns, leaving him alone before he is obscured by the fog.
Cut back to the portals where Desna and Eska approach the frozen Mako and Bolin.]

Mako: Please, let us out.

Desna: His grovelling is pathetic.

Eska: But I do enjoy the sweet scent of desperation.

Mako: Come on, your dad has become an evil monster. He's gonna bring on eternal darkness. Why would you protect someone who doesn't care about you at all?

Desna: [To Eska.] Father was going to let me expire when we tried to open the northern portal. Perhaps we should rethink our position.

Mako: Yes!

Eska: No. Don't listen to him. His words are poisoning your mind. [Bolin weeps bitterly.] What's with this outburst of emotion?

Bolin: [Weeping.] I'm sorry, I can't help it. It's just so sad that I'll never be with you again.

Eska: What? Explain yourself further.

Bolin: Eska, I've always loved you. And I always wanted to be with you. But now that the world is ending, [Weeps.] I'm never gonna get that chance.

Eska: [Angrily.] We could have been together, but you left me at the altar.

Bolin: No, I was scared. I was scared of my true feelings for you. Gah, I should have never left you. I'm sorry. And I'm sorry that we'll never have the chance to rekindle the dying ember that was our love into a big fire of love flames.

[As Bolin continues weeping, Mako looks on with unsure looks. Eska looks at Bolin with confusion before kissing him. The ice around the brothers melt. Eska stops kissing Bolin.]

Eska: You'll never defeat my father. But, should you survive, perhaps we could spend eternal darkness together.

[Mako taps Bolin on the shoulder before both brothers run away.]

Mako: Wow! That was the best acting I've ever seen. You completely fooled her.

Bolin: [Unsure.] Yeah right, huh. That was acting. [Wipes a tear.]

Desna: They will certainly perish.

[As the brother run out of the portal into the South Pole, they witness the two Avatars fighting. Korra shields herself from Unalaq's water attacks with fire before exiting her air spout. On the ground, she directs three rocks, knocking Unalaq off his waterspout. Unalaq manages to remain in the waterspout and direct two water streams at Korra, which she manages to nimbly dodge. Korra propels herself with earthbending and throws three fire blasts at Unalaq. Unalaq throws a large water whip at Korra, which she manages to catch, before freezing it and tossing him off his waterspout. Korra bends out another water whip and traps Unalaq's left hand. Unalaq enters his Avatar State and pulls Korra toward him. The Avatars drags themselves toward the center. As Korra enter the Avatar State, the show of strength resulted in the ground around them to rumble and crack. Cut to Unalaq, where Vaatu emerges from within, startling the brothers. Korra attempts to attack Vaatu with a fire breath, but Vaatu enters her mouth and pulls out Raava. Korra weakens and collapses onto the ground. Cut to Korra's point of view where she weakly notices Unalaq trapping Raava in a water bubble. Cut to Unalaq where Vaatu re-enters his body, and he grins viciously.
Cut back to the Spirit World where Tenzin is trying to keep himself sane.]

Tenzin: You must stay focused. Remember who you are Tenzin. You are the son of Avatar Aang. You are the hope for future generations of airbenders. The fate of the world rests on your shoulders. But what if I fail? [Looks around.] Then your father's hopes of the future dies with you. I can't fail. You will. [Covering his ears, while sagging to the ground, arguing with himself.] Ah, stop it! I am the son of Avatar Aang. I am the hope for future generations of airbenders. I am the son of Avatar Aang. [Hallucinating, he looks up to see an image of his father standing before him.]

Aang's image: [Appearing from the fog.] Hello, my son.

Tenzin: Dad, [Sadly.] I've failed you. I am no spiritual leader, and I've let the world down. I'll never be the man you were.

Aang's image: You are right. [Tenzin is shocked at the revelation.] You are trying to hold on to a false perception of yourself. You are not me and you should not be me. You are Tenzin.

[A puff of smoke engulfs Aang, when it disappears, he becomes a reflection of Tenzin. Tenzin stares at his reflection and gives a determined look before standing up.]

Tenzin: I am not a reflection of my father. I am Tenzin. [With his reflection.] I am Tenzin!

[As Tenzin speaks, a glow of light illuminates the sky, dissipating the fog. Tenzin looks on in amazement and scans the surroundings for his daughter.]

Tenzin: Jinora!

[Tenzin hugs his daughter, who was kneeling dejectedly before carrying her. He finds his elder siblings, who have succumbed to the effects of the fog, and leads them out of the valley. When they exit, the fog returns.]

Bumi: [Dazed and confused.] Huh? What happened?

Kya: I think our brother saved us.

Jinora: Dad. [Hugs her father.]

Tenzin: You'll be okay sweetie. I'm here.

Jinora: [A light butterfly spirit flies onto her arm.] What happened? The last thing I remembered was dark spirits taking me away.

Tenzin: You were trapped in the Fog of Lost Souls. And I wasn't going to let you stay there.

Jinora: I'm so happy to see you, Dad.

[Two more light butterfly spirits fly onto Tenzin and Jinora. Bumi and Kya join in the hug.
Cut to the South Pole where Unalaq prepares to attack Raava.]

Mako and Bolin: Korra!

Bolin: He's got the Light Spirit!

[The brothers prepare to attack Unalaq, but the Dark Avatar easily neutralized their attacks and sends out a large ice spike, knocking Mako and Bolin unconscious.
Korra weakly attempts to reach Raava, but Unalaq picks up the spirit with purple streams of water and slams her against a rock. He directs a strong blast of water at Raava. Cut to Korra as she groans in pain when Avatar Aang disappears from her vision of the Avatars. With another strike, Korra's vision of Avatar Roku disappear. The following strike destroyed Korra's vision of Avatar Kyoshi. Korra weakly tries to get up, but another strike on Raava causes her to shrink in pain as her vision of Avatars Kuruk, Yangchen and the unknown Fire Nation Avatar disappear. The next strike led to multiple rows of Avatars being destroyed. Unalaq bends out another stream of water, preparing to attack. Korra futilely tries to muster sufficient strength. With one final blow, Raava was destroyed, dissipating in a glow of golden light, and Korra's vision of Avatar Wan disappears. Korra struggles to muster sufficient strength before passing out. Unalaq subsequently turns dark, with Vaatu's patterns on his chest, and grows slightly in size.
Cut to the Spirit World where Tenzin, Bumi, Kya and Jinora prepare to leave. Jinora, however, stops and turns back.]

Jinora: The world is in trouble.

Tenzin: What are you talking about? How do you know?

Jinora: I can feel it.

Bumi: What happened?

Jinora: It's Korra. [Passes a light butterfly spirit to her father.] This light spirit will guide you out of the Spirit World. I have to go help. [Fades away.]

Tenzin: Jinora, wait!

[Tenzin reaches out for Jinora, but she disappear before he could. Bumi and Kya look on in surprise.
Cut back to the South Pole where Mako and Bolin pick up an unconscious Korra. The turn to see Unalaq growing in size. Cut to Desna and Eska who exit the portal to find their father growing to large proportions, looking on in fear. Cut to Unalaqs point of view where he looks at Mako, Bolin and Korra while growing in size.]

Unavaatu: Now, ten thousand years of darkness begins!

[Cut to Unalaq reach out to the spirit lights, creating a storm. Cut to Mako and Bolin who look on in fear and worry. Cut to Unalaq who teleports away, creating an impact that tossed Mako, Bolin, Korra, Desna and Eska away. Cut to a close-up of an unconscious Korra.]

[Fade to credits.]