That's as far as I wrote. The rest is a summary. Until the last scene.
Cut to the Doctor and Braxiatel, setting the whole thing up.
It's important, for the sake of the story, to remember that the Doctor has just learned about Elizabeth destroying the Earth to escape her UNIT prison. That happens to be foremost on his mind, right now.
Daleks nearly catch them, but the Doctor and Braxiatel evade the Daleks.
They power everything up and switch the whole thing on. For a few seconds, they think it's going to work. The machinery spirals out this beautiful vortex, and both the Doctor and Braxiatel can see the timeline isolating and the remap beginning, exactly as Braxiatel had planned.
Then the energy runs out.
Turns out, the energy field wasn't half-depleted, it was completely depleted. Without that, they can't tap into the Key to Time's power properly, and the whole thing starts to self-destruct.
The Doctor and Braxiatel frantically try to jury-rig the system, so it'll work.
"I found it!" Braxiatel realizes, as he sorts through timelines with his Epoch technology. "A diverging point. A place of unspeakable energy!" He rewires everything so he can tap into that. "Feed that to the Key to Time, and…"
"No, wait!" the Doctor shouts, lunging for Braxiatel. "It's unstable. It'll…!"
The whole thing explodes around them both.
The Epoch technology fuses with the timeline isolation technology, and a sudden rush of power from the Key to Time activates them both and floods the system. Psychic feedback from the Epoch technology combines with temporal and pan-universal feedback, and both the Doctor and Braxiatel get swept up by it.
Braxiatel, his mind plugged into the system, passes out.
The Doctor tries to save the situation, but winds up instead connecting himself into the machine. It grabs at his guilt over what Elizabeth did, on Earth, and also plays on his fears about what the sisters of Khan predicted that the Doctor would do at the end of the war.
Since these two events are at the foremost of the Doctor's mind, the Epoch technology fuses those two sections of time together, and remaps them accordingly.
Remember what we saw in Paradox? The Doctor, in the middle of the destruction of Gallifrey, wishing that he could change the past and get another chance with Elizabeth?
That scene is actually happening now. Not at the destruction of Gallifrey.
The Epoch's machinery plays through an entire potential timeline, in which the Doctor actually does use the Moment. When the Doctor wishes that he could fix things back on Earth, the Epoch's machinery responds to his wish and remaps Elizabeth's entire life — turning her into Buffy.
Precisely as we saw in Paradox.
The result?
Instead of remapping Gallifrey, Braxiatel's plan remaps the Doctor and Buffy.
When the Doctor snaps out of this, and realizes that the machinery has failed, he tries to find Braxiatel. But can't. He eventually comes to the conclusion that the plan backfired, and Braxiatel is dead, as a result.
The Doctor receives word that the Daleks are about to pass the transduction barrier, on Gallifrey. He races back, just in time to fight at Arcadia.
Romana, meanwhile, is fighting at the Battle of Arcadia. She soon meets up with the Doctor, and discovers that Braxiatel's plan has failed.
The Doctor terrifies Romana, at this point, because he's so obviously lost it.
The Doctor's been pushed to his limit and is willing to do something drastic.
When Arcadia falls, Romana realizes that the Doctor's completely snapped. She runs off, grabs a TARDIS, sneaks past the Daleks, and heads off to find Braxiatel.
If there's anyone who can convince the Doctor not to use the Moment, it'll be Brax!
Romana searches through the time anomaly that Brax's failed plan has created. Drawing on knowledge from her many times trapped in other time anomalies, she manages to locate him.
"Brax!" Romana shouts, shoving rubble off of him. "Wake up!"
Braxiatel groans, and awakes. He's been trapped in a pocket of time, and under a lot of rubble. He's injured, but can still walk.
"It… didn't work," Braxiatel realizes. His hearts sink. "If I'd only had more time…"
"Enough of that!" Romana shouts, helping him to his feet. "Arcadia's fallen. The Daleks are taking the capital. And I think the Doctor's about to do something terrible!"
The time pocket begins to collapse, around them. And Braxiatel and Romana scramble to get out of it before they're crushed out of time and existence.
"The Doctor?" Braxiatel asks. "Rassilon, surely. The Ultimate Sanction."
"No, the Doctor!" Romana says, as they enter her TARDIS. "He has the Moment." She slams the doors shut, launches them into the vortex. "And I think he's going to use it — on Gallifrey."
"What?!" Brax cries.
To get back to Gallifrey, they have to run the Dalek blockade — which is now even harder to run now than before, as the Daleks have increased their defenses. Romana almost fails, but Braxiatel — due to his time at the Collection — has experience with running blockades.
(Almost every single time the Collection was involved in a war, Braxiatel's had to run a blockade! He's very good at it.)
They emerge onto the surface of Gallifrey, but Romana doesn't have a clue where the Doctor would go to set off the Moment. Braxiatel, being the Doctor's brother, does — and together, he and Romana start running towards the barn.
Half-way there, Romana receives a message from Rassilon, saying that he's ready to put the Ultimate Sanction into place.
"I have to get to the capital," Romana says. She turns to run the other way. "You find the Doctor. I'll take care of Rassilon."
Now we encounter a scene that Braxiatel saw, before. Because the Moment showed it to him. This is the scene:
Braxiatel realizes that Rassilon will kill Romana if she returns to try to stop him. And he knows that, if he saves Romana, he'll never make it to the Doctor in time.
Braxiatel hesitates.
It's a choice between Gallifrey and Romana.
But he knows, already, which one he's going to save.
Braxiatel knocks Romana unconscious, and drags her back into her TARDIS. He knows that either Rassilon's plan will succeed, or the Doctor's, so he tries to shield Romana's TARDIS against both, hoping to send her off Gallifrey and away to somewhere safe.
He runs out of time.
There's a feeling like Gallifrey is exploding and burning all around them. It even sears into Romana's TARDIS, through all the defenses.
Braxiatel takes what he thinks is his last breath, as he tries to save Romana.
There are two alternate versions of history that happen, at this point in time.
In one, Romana awakes just in time to see her planet dying, around her. She sees Braxiatel, already dead, his burned and charred corpse slumped over the sparking and melting control console. And outside the doors, she sees the planet burning.
Then Romana dies, too.
That's one version.
In another version, Braxiatel takes another breath. And another. And another.
Then, after a while, he realizes that he isn't dead and Gallifrey hasn't exploded. But something has certainly changed. He can feel the way the planet moves through space and time, feel the relationship of Gallifrey against the timelines. It's all different, now. Nothing has burned — even if he thought it had, just for a moment.
Romana wakes up. Furious at Braxiatel.
"What is the meaning of this?!" Romana demands. She climbs back to her feet. "I swear, Braxiatel, if you've dragged me in here just so you can run away from this war and save your own skin, I'll—!"
Braxiatel steps outside.
Romana does, too.
"That's… impossible!" Romana says, looking at the stars.
But it isn't. Gallifrey has moved.
The Doctor has saved it.
Gallifrey, present-day
"Romana and I returned to Gallifrey," Braxiatel summarized, carefully editing the real story. "We tried to stop the Doctor. But in the end… I suppose I just wasn't fast or clever enough to find him, in time. That's what the Moment showed me."
"But it didn't matter," Jenny insisted. "Because Dad saved Gallifrey."
Braxiatel sighed. "And look what we've done with it, since!" He stood up, walking over to a large glass window that showed the Gallifreyan landscape. His eyes drifting over snowcapped mountains and red earth. "Riots and disarray. Rassilon's tyranny. The renegades trying to strike back at a world that rejected them. And the Victor, of course…"
Jenny stepped up, beside him.
She wasn't looking at the landscape.
She was looking at Braxiatel.
"You've never told Romana, have you?" Jenny asked, quietly.
Braxiatel spun around, a little flustered. "Haven't told her what?"
"That you're the one," said Jenny, "who's been betraying her to Rassilon. Ever since the planet got moved. And all the time I've been here."
Braxiatel said nothing.
"Someone on the inside, Romana said," Jenny continued. "Someone she really trusts. Someone who's been quietly telling Rassilon everything he needs to know… so that Romana's always two steps behind Rassilon's plans."
"Jenny…" Braxiatel began.
"Because Rassilon's threatening her," Jenny prompted. "Isn't he? Threatening her… to ensure your cooperation. At a guess — he did it during the War, too. The hidden motive behind your story."
Braxiatel couldn't answer this.
"I always thought it was funny that Rassilon's let Romana have free rein," said Jenny. "Especially since he's been systematically destroying or silencing all his other political rivals. Whatever you're helping him with… it must be something important."
"So he supposes," Braxiatel replied.
Jenny looked at him, strangely. And it was clear — she knew he had a plan up his sleeve.
But Braxiatel knew better than to reveal that plan, before he'd ensured his own success.
"Are you going to tell Romana?" Jenny asked. "What really happened, at the end of the war?"
Braxiatel returned to his desk. Placed something secret in a drawer, closed and locked it.
He doubted Romana would thank him for what he did.
"That I was prepared to sacrifice Gallifrey for a single person?" Braxiatel looked up at Jenny. "Some things, Jenny, are best kept secret."
He tucked the key away, into a pocket.
And returned to his work.