Prompt: "Thriller" by Michael Jackson

Characters: Zuko, Aang, Mai, Koh

Pairing: None

Something was lurking in the dark—and what was worse, even what little information he did have told Zuko that he was powerless to stop it.

"Aang, can't you tell me anything else about this… spirit?" When several Fire Nation citizens had shown up missing their faces, Zuko had known right away that it was out of his hands, and he had done the only thing he could do: he had sent for the Avatar immediately. Close to midnight, Aang had arrived along with Sokka and Katara, and they must have been hurrying like mad to get here so soon—that sort of urgency was never a good sign.

Now, Aang was telling him that there was some face-stealing spirit on the loose, and that the only defense against it was to show no expression at all. It grated on Zuko that he would not be able to face this Koh—it might have been the Avatar's job to maintain balance with the Spirit World, but those were his people out there suffering a fate worse than death. As their Fire Lord, he should have been able to protect them.

"I… I don't know." Aang bit his lip as Katara and Sokka slid from Appa's saddle behind him. "Koh steals faces. I never asked him why, and I don't know what he's doing out of the Spirit World now. I'm going to go talk to him and see if I can find out what he wants."

"Do you need any help?"

"No!" Aang looked slightly panicked for a second before he forced himself to calm down, taking deep, even breaths. "If you show any emotion—anything, no matter how slight—the same thing is going to happen to you. I've got several hundred lifetimes' worth of experience to draw on to keep my face blank, but I can't know that you can do the same, and I'm not putting you at that kind of risk unless I can be sure. Besides, you need to focus on getting people to safety—Katara, Sokka, and Appa will help you."

Of course, Aang was right—as usual. Zuko gave a nod, and Aang tossed him the reins before taking up his glider.

"What are you going to do?" he could not help but ask as his friend stood on the edge of the palace balcony, looking out into the darkened city.

"I'm going to talk to him, and find out what he wants. Maybe I can convince him to stop." Still, Aang did not look at him as he said it, but whatever he was planning, there was nothing Zuko could do—his responsibility, first and foremost, was to his people.

"Okay. Be safe."

Aang nodded back. "Good luck."

Mai's heart gave an unpleasant jolt at the sight that greeted her by the light of the full moon.

The thing looked like a spider-centipede gone wrong, mutated and grown to enormous size. Even worse than that, however, was the fact that the thing was currently staring at her with her mother's face.

The scream of terror that wanted to come out of her mouth got caught and died somewhere in her throat, and Mai could only stand, paralyzed, as the thing met her eyes and moved toward her with a predatory grin.

"Why hello, young lady." It did not speak with her mother's voice—its tone was much deeper, more masculine—but the sight of her mother's face alone was enough to prompt Mai to unconsciously school her own face into an impassive mask, to avoid showing even the slightest hint of an expression even as it coiled about her and came just short of tapping her shoulders with its many legs. "And what is a noble girl with such a beautiful face doing outside by herself in the middle of the night?"

"Nothing. I just hate it less out here than I do inside." Mai had adopted her "bored tone," her personal passive-aggressive shield against her mother's constant admonitions to sit still and be silent, to never do anything unbecoming of a lady—in other words, never to do anything at all. In truth, Zuko had asked for her help in evacuating some of the more vulnerable families while he awaited the arrival of the Avatar—but the truth, in this case, would only be a liability, would be handing the enemy weapons. She did not have to be a genius or a spiritual expert to deduce that this monster bore the responsibility for the nightmare that had engulfed the Fire Nation capital.

Its face blinked closed, and when it opened again her mother's face had been replaced with a new one, an elderly man she didn't recognize. "You do not look very hateful." It tightened its coils, peering into her eyes before circling around to her back, but Mai kept her face determinedly blank. "As a matter of fact, you do not look anything at all."

"So?" She wanted to shrug, but resisted the urge—the thing was wound around her body rather tightly now, and the thought of brushing up against its legs was one that Mai found rather repulsive. "What do you care how I look?"

"Koh." Both of them turned at once, to see the Avatar standing in a nearby alleyway, glider in hand—and, Mai could not help but notice, his voice was level when he spoke, his face perfectly devoid of any expression. "What are you doing here?"

"Ah. My old friend the Avatar." To Mai's relief, the creature uncoiled from around her body and slithered in Aang's direction instead. "To what do I owe this visit?"

Instead of answering, the Avatar turned to Mai. "Go find Zuko and the others. They're evacuating the city." He waited for her nod before returning his attention to the monster—Koh, Aang had called him. "Why don't you answer my question first?"

As she fled down the nearest available alleyway, the last thing she heard was Koh's response: "What am I doing here? Someone called me, of course."

"Listen up, everybody! We need to do this in an orderly fashion! Children and the elderly on Appa! Everyone else, go with my sister."

The people scrambled to do as Sokka instructed, parents handing their children up to Appa's saddle. While he was busy with that, Katara helped up a pregnant woman and a man missing one of his legs. As soon as they had crammed up as many people as they could manage, Sokka settled himself on the bison's neck, but it wasn't nearly enough: they were still surrounded by people on the ground, families, disabled, people who would not be able to run even if their lives depended on it.

There was nothing for it, however: Appa's saddle simply would not fit any more people. "Go," Zuko said. "The sooner you get moving, the sooner you can come back for more. We'll handle things on the ground."

With a nod, Sokka flicked the reins. "Yip yip."

Appa beat his tail against the ground, and then they were airborne. Katara continued to watch until the bison was nothing more than a tiny white speck in the distance.

Meanwhile, Zuko was walking among his people, walking from one to the other and speaking words of encouragement. "Stay calm. They'll be back shortly." Katara, however, kept her eyes on the skies, and before long she saw what she was waiting for: another speck, not nearly large enough or white enough to be Appa, came flying down at them, and she held out her arm to intercept it.

Sokka's messenger hawk lighted on her leather gauntlet, and she reached into the message tube on its back to read their latest intelligence—from a high elevation over the city, Sokka would be able to track Koh's movements without taking the risk of losing his face. "He's in the northwest quadrant," she informed Zuko, "heading toward the caldera wall."

Zuko looked up, startled, from where he was trying to help a woman calm a screaming baby, as Katara released the hawk once more. "Then we need to move." He straightened, assuming the same clear, confident tone that he used when giving a public speech. "Everybody. We're going to head south now. Stick together and stay calm!" Even as he spoke, he shot his fist into the air, producing a string of characters, written in flame, which hovered in the air for a few seconds before dissipating into smoke. Hopefully, that would be enough to inform any stragglers of their new location.

As the crowd began to move, Zuko took the lead while Katara brought up the rear. Her hand hovered constantly over the mouth of her waterskin, even though she honestly didn't know whether even her bending would be able to protect her—not against a face-stealing spirit who needed only an expression in order to render her worse than a corpse.

They had walked for what seemed like hours, her feet sore and her legs burning with the strain, when she heard movement to her side. Immediately she tensed, feet moving into a fighting stance.

"Hello?" she called. For all she knew, the movement could have been a person, yet another innocent civilian trying to get out of the capital before falling victim.

Something moved at her out of the dark.

Instinctively, forgetting what she was doing and what the situation was, she turned—but before it came into her line of sight, a wall of flame sprang up between them, blocking it from her view and her from its.

"GO!" Zuko yelled, the good side of his face twisted in panic, and the flames roared higher. "Take the others and run!"

"But you—"

"Katara, the people need someone to protect them! I'll hold him off, but you have to go now!"

Swallowing back her hesitation, Katara nodded. Already screams of panic were erupting around her, but she raised her voice above them. "Everyone with me! Now run!" As she spoke she emptied her waterskin onto the ground, at the same time drawing moisture from the gutters, from the air, from people's sweat—anywhere she could reach it, and leaped forward onto the puddle that froze at her touch. The others followed suit, and then she was carrying them along on a wave of ice, out of the capital and toward the distant edge of the caldera. As they traveled, tears streamed from her eyes, but she did not bother to wipe them away.

I'm sorry, Zuko.

Turning his head, he saw that Katara and the people she protected were already far into the distance. Good. He had bought them enough time.

That said absolutely nothing, however, about Zuko's situation. Even as he looked after Katara, he saw a dark shadow moving through his flames in his peripheral vision, and braced himself. Show no expression, Aang had said. Aang had also said that he didn't know whether Zuko could pull it off, but that didn't mean he shouldn't at least try. Before he could school his face, however, the dark form had moved out of the flames entirely.

"Hello, Fire Lord."

Zuko knew that he was showing shock—he had had no time to adopt a calm expression. By all means he should have been a faceless worse-than corpse the moment Koh broke through the flames, yet somehow—face! That was it! He was presenting Koh with his left profile—the eyebrow missing and the eye frozen into a permanent glare by the hardened scar tissue. As far as that region of his face was concerned, he couldn't have emoted if he tried.

Now, he only had to be extra careful not to smile or frown—or smirk, grit his teeth, gape… okay, maybe he wasn't out of the fire yet after all.

"Hello, Koh." As the spirit circled around him Zuko turned so the left side of his face was always facing him, though it screamed against every instinct he had—his eye had been injured by the burn as well and had never fully healed, leaving his vision much weaker on that side than it was on his right. Currently, all he could make out of Koh was a dark blur.

"My reputation precedes me, I see."

"You do know that the Avatar is here, right?" Zuko turned once again; he must not let Koh see the right side of his face…

"Oh yes. I ran into him myself, a little way back. He tried to stop me, but I don't have nearly enough faces for my collection yet, so I'm afraid that returning to the Spirit World will have to wait."

"So why do you want faces?" Buy time, buy time, just keep buying time until Aang figures something out…

"I really don't think a human would understand the why of what I do. If you are not amenable to giving me your face, however, I suppose I will simply have to find someone more… emotional."

Katara! The horrified realization had barely hit him, however, when Aang's voice called out to him out of the dark.

"Zuko! Stand back!"

He barely had time to leap out of the way as Aang landed between them, a wind springing up around him as his eyes and tattoos lit up with a supernatural glow. "Koh the Face Stealer," he said, and when he spoke it was no longer in Aang's voice, but in the combined voices of all the Avatars before him. "You are devastating the balance of the human world and the Spirit World. Return to your home, and leave us to ours."

At that, the light glowed so bright that Zuko had to look away, his eyes squeezed shut. When he looked again, Koh was gone—and Aang was once again just Aang, panting with exertion as he leaned on his glider.

Slowly, they both sank to the ground, leaning against each other as they sat back to back. "I hope… I never have to deal with anything like that… ever again."

"How did he even get here anyway?" Zuko asked. "And why?"

Aang rubbed the back of his head, looking sheepish, which Zuko knew was never a good sign. "Um… well, he said that someone summoned him. I un-summoned him just now, but we're going to find out who did it in the first place, and how, so that it doesn't happen again."

Zuko leaned back with a groan. This, he knew, was his job—and after a night like this, he never wanted to hear about spirits ever again.

A/N: This is the last official chapter, and... yeah. I'm not happy with it. I found this one especially hard to write, primarily because I've already written a Thriller-inspired story for another fandom, so my inspiration from this song all went into that story, leaving no room for this one, and if I want to stick to my one-a-day self-challenge, I have to post what I've got. Anyway, as fun as it's been, it'll probably be a while before I accept another fanfiction challenge like this.