"Clara." The Eleventh Doctor spoke.
"Hm?" The Brunnete asked, as she was sitting in the TARDIS, about to read a book."
"Do you want to hear a story?" He asked.
"Sure, Doctor." Clara replied, putting down her book.
"It's about two great friends, and how one simple conflict had broken their friendship." The Doctor replied sadly.
"Ok." Clara replied.
"So long time ago, these two people who could bend fire. One was a firelord, and the other was another firebender. Except, this firebender was not an ordinary firebender. He was a being known as an Avatar, a person that can control all four elements at will: Earth, Air, Water, and Fire. All together at once. So the two people were friends until they got older." The Doctor explained, and then he stopped.
"What happened after, Doctor?" Clara inquired.
"One simple conflict broke their friendship, and ignited a war for many years. Fortunately, the new Avatar ended it with the help of his friends and the new Firelord." The Time lord replied.
"What conflict?" She asked.
The doctor took a breath. "Roku, the Avatar, saw what his friend, Sozin was doing. He was trying to take over the world. Roku obviously didn't like this, and engaged him in combat. But there was one moment where the two settled their differences."
"Hm?" Clara asked.
"Roku's house was burned by the volcanic eruptions on the volcano it was standing on. Sozin came on his dragon to help him. However, in the end Sozin betrayed him." The Doctor turned the other way.
"Why?"
"Because he was selfish. But I tried to stop him, make him consider his actions." The Eleventh spoke.
"Sozin, help me." Roku choked as he consumed the horrible vapors of the volcano.
"With you gone, Roku, I will have no trouble in conquering the world." Sozin said.
"Don't you realize what you're doing?" The Tenth Doctor shouted.
"Who are you?" The Firelord spat back.
"I'm the Doctor." The Doctor replied defiantly. "And I know what's going to happen next."
"Well Doctor, all I know is that, I will rebuilt an empire like no other." Sozin declared.
"Your friend is dying here!" The Tenth said, as he pointed to Roku. "Don't you think it's wise to help him up?"
"He's no friend of mine." Sozin spat.
"You're making a big mistake, Sozin!" Doctor shouted. "But we can stop an endless war from happened. Please Sozin, be friends with Roku! At least obey his wishes. The World doesn't want to be conquered."
Sozin had enough of this Doctor. He threw a fireball at him, and the Doctor dodged that attack.
"I don't care about the world, Doctor! There's one thing about the world! It's needs to be conquered!" Sozin shouted, as he began to leave.
"Have it your way then, Sozin." The Doctor spoke sadly. He turned to Roku. "I'm so so sorry. Really I am."
"Help me, Doctor. I'm dying." Roku choked.
"I can't help you, my friend. But there will be hope. The next Avatar will stop the Fire Nation. His name is Aang, and he's from the Air tribe. You'll meet him later in the spirit world." The Doctor said, as he left in the Tardis. The Tardis began to dematerialize, as Roku and his dragon were engulfed in the flames of the volcano.
"Why didn't you help him, Doctor?" Clara asked.
"Roku dying was a fixed point in time. He was old anyway, and he wouldn't able to stop Sozin in time. That's why I had to let him die." The Doctor replied.
"Also one question, Doctor?"
"Yes?" The Time lord asked.
"How do you know all this stuff?"
The Doctor smiled happily. "I got the tale from the fire elders. The TARDIS took me there for some strange reason. I don't know."
"Doctor, you're a mad man sometimes." Clara said.
"Yes, Clara. I'm a mad man. A mad man in a box." Doctor replied.
"Now where to, Clara?" The happy Doctor asked.