Author's Note: Okay, because this has come up twice so far, I'll just give a bit of background about the Key to Time in the Doctor Who universe.

In the Doctor Who universe, there are six segments of the Key to Time. Each one possesses special and unique abilities at particular points in space and time. Together, they form something powerful enough to completely stop and start the universe (something that is far more powerful than anything you or I could imagine, basically). The segments do not look like segments, but are disguised as something else, all throughout space and time. Each segment can be disguised as anything - or anyone. The Princess Astra, for instance, was actually a segment of the Key to Time (although she didn't know it).

Now, the Key to Time is older than anyone really knows, and possibly as old as the universe itself, but its presence on Earth is a bit spotty. It was actually being stored in a hyperspacial anomaly, which means that the only thing that was actually on the planet itself was energy. I'm guessing a great big amount of shiny green energy. And when the Doctor took that particular segment of the Key to Time away (in the late seventies), all that was left on Earth was the energy. This energy will, eventually, become Dawn - one segment of the Key to Time (the seventh segment, and no, there isn't supposed to be a seventh segment).

Problem is, the Doctor will not admit it, but the Key to Time (all six segments, assembled) is actually still out there. Don't want to give away too much of "Time Walker", for those who want to read it. But there is something going on with energy and the Key which makes the Monks able to create Dawn.

At the moment, Dawn does not exist except as a potential temporal probability. However, the Key to Time does exist. And the Doctor knows where it is and how to get it.

This is also explained in "Time Walker". If you want more information, you should probably read that fic. As I said before, you don't have to, but you're going to have to do a lot more guesswork if you don't.

Hope this clarifies things.

Buffy stared at the Doctor, at Omega, at the soon-to-be-open portal. No. No, that didn't make sense. Omega had been trying to kill her. He'd been so angry that she hadn't died already. Then he'd nearly killed the Doctor. And now he was trying to create some evil inter-dimensional portal. He was evil. He had to be evil.

"What?" cried Jack. "You said he was letting Toby in!"

"He is," said the Doctor.

"And he's also keeping Toby out?" said Buffy.

"Yes."

"He will come through, Doctor," shouted Omega. "The Origin of All Evil will be here, and you will serve him!"

"Do you want that, Omega?" asked the Doctor. "Is that what you really want?"

Omega blinked, and suddenly, he was back to being that frightened, trembling, desperate creature from before. "I… I…" He swallowed. "I don't…"

"You're confused, Omega," said the Doctor, in that calm, soothing tone of voice that he'd used earlier. "You're confused and frightened, and you don't know what to do. You have too many voices in your head and you don't know which to follow. All my old regenerations. All your old regenerations. And then there's that extra little nasty voice inside your head, that hateful little voice that's been trying to get you to let it through. And it's confusing, all those voices telling you to do contradictory things. In the end, it's enough to make you question who you really are."

"No!" Omega shouted. "I know who I am. I am Omega! Creator of the Eye of Harmony, founder of… of…" His face seemed to crumple. "You killed it, Doctor!" he screamed. "You killed them all!"

"I had to," said the Doctor. "We all have to do things we don't like. We all have to make choices we don't want to make. Even you."

"You… you…" Omega threw his hands to his head, as if in pain. When he spoke again, it was with an angry growl. "You should die, Doctor! I should kill you!"

"That voice in your head," continued the Doctor, soothingly, unaffected by the threats, "it's been telling you all the things I've done, all the reasons you should take revenge. But you know as well as I do that revenge is never going to get them back, Omega. Revenge can never undo what's been done."

"Revenge will fix everything!" insisted Omega.

"That what that little hateful voice inside your head's been telling you?" asked the Doctor.

"I will destroy it all, I will make the universe fear the name of O… O… Omega…" Omega faltered. "It's not fair! I have to get out, Doctor. I have to get out!"

"I'm sorry, Omega," said the Doctor. "You can't get out. And you know why."

Omega hung his head, looking almost like a chided student. "If I get out, he gets out, too," Omega whispered.

"And you've been trying to keep him away from here," said the Doctor. "You're a good person, Omega. You'd never let something like this happen."

"You put him in there," Omega accused. "You locked him up with me. It should have been you! It should have been you!"

The Doctor's face clouded. "Yes, it should have," said the Doctor. "But it wasn't. My going in there will solve nothing. It'll only make things worse. In the end, you're the only one who can fix this. You're the only one who can make sure Toby stays out."

Omega was staring at the portal, trying to decide. He was wavering, hesitating, trying to get up the courage to do the right thing. Buffy was holding her breath. She wasn't completely sure she believed her eyes or ears. She was watching the Doctor talk a villain into doing the right thing. He wasn't killing the villain or beating the villain up. He was just… talking. And the weird thing was, it was working!

Omega took a step forward, paused, then seemed to huddle in on himself. "Can't," murmured Omega. "Can't go back there. Don't make me do it!"

"I know you're frightened," said the Doctor, soothingly. "I know what you've gone through already. But you know what's right. You know what you have to do. You've created a potential hole in the universe, a probability that's becoming increasingly more stable over time. The only way to seal it is to close the breach on both sides. I will help you, Omega, but you have to help me."

Omega huddled, whimpering, on the stage. "You don't know what it's like back there," he said. "I see them, Doctor. Every day. Ten billion people and they are screaming. So loud! Screaming and burning! They know what you did, Doctor! They know what you did!"

"They aren't real, Omega," said the Doctor. "You don't have to feel guilty. It's my guilt, my responsibility. Be remembered as the one Time Lord left in existence who did the right thing. The one Time Lord left who had the courage to make the right choice."

Omega stared at the Doctor. "No, they're real! I saw them, I heard them, they…."

"They're like the Scintillans," said the Doctor. "You've blamed yourself for killing them, and the guilt is making them seem real. But they're not. And they shouldn't be. You didn't destroy them, Omega. I did. You don't have to blame yourself for this. If you stop the blame, they'll go away."

"They're real," said Omega. "They're all back there. Waiting to torment me."

"I know it's not easy," said the Doctor. "It's never easy to do the right thing. Everyone here knows that. But we believe in you. We all believe that you have the strength to do this. To make things right. Go back, seal the breach from the other side, and keep Toby out of the universe." The Doctor gave a long, sad smile. "Be the hero, Omega, the way you always were. Let me be the villain."

"I can be a hero again," said Omega. "The way I was before. The way I was on Gallifrey, before I ever met you. I can be remembered for greatness."

"You can."

Omega got up, a determined look on his face. He took a few steps forward, towards the portal, but then he faltered, slowed, and stopped. His shadowy hands were shaking, as he stared at the portal with open terror. "No… no…." He stepped back. "I don't have to go back, Doctor! I can still be a hero out here. I can keep him out from this end. The energy I've built up, it will be enough."

"It won't be enough," said the Doctor.

"It can!" insisted Omega. "I can find more. I can—"

"It'll never be enough," said the Doctor. "Do the maths, Omega. The energy required approaches infinity over time. If you remain here, if you don't seal the breach, nothing in the universe will have enough energy to keep Toby out. Not even the Key to Time."

Omega's desperation and fear fell away at those words, as he stared at the Doctor, realization washing across his face. Not just realization, but relief — an overpowering sense of dark, deep relief. As the relief grew, a cruel maliciousness seemed to ripple through Omega's smoky body.

The Doctor's brave face faltered, just a hair.

And Buffy knew, with a sudden, icy clarity, that the Doctor had just said exactly the wrong thing.