The First Companion
He'd decided to go and see all of his former companions and that meant all of them. He'd gone in order of when he met them, minus Rose, of course. Rose was the first face this face saw; she deserved to be the last.
Arkytior. His Susan. There were a million reasons he shouldn't see her- but he would anyways.
The only thing he could do to create more of a paradox would probably visit Trensalor, where he heard he was buried. Even the Doctor wasn't that stupid.
But he was just stupid enough to keep his promise. Just stupid enough to go back.
It had only been a few years since Susan had been left there by her grandfather, for her at least, but for the Doctor 500 years was more like it. He'd always meant to keep his promise and return, but the time had never seemed right. Now it was and he could delay it no longer.
The Doctor found his granddaughter in a house only a block away from where he locked her from the TARDIS. Susan and David sat out on the front porch like your classic human couple despite the fact all around them Dalek carnage had yet to be cleared. The Doctor left Susan to rebuild Earth which she would, but from the baby in her arms and the toddler running on the grass she'd been a bit too busy to do much of anything.
The Doctor knew he was old, but the thought of looking in his late 30's and being a great-grandfather startled even him. Still, smiling at the bright half-Gallifreyan half-human the Doctor had hope that maybe his metacrisis self and Rose would be able to raise the family they wanted.
Don't think about Rose. The Doctor told himself. That time would come very soon, now was about Susan.
"I don't know you," Susan called from the front porch as she handed the infant to David and made her way over to the Doctor. "And I thought I knew everyone in this wreck of a city I call home."
"I'm new," the Doctor told her suddenly deciding not to reveal his real identity. "I'm not exactly from around here."
"Oh that's certainly true." The Doctor had forgotten that his daughter, Susan's mother, had an inert ability to recognize other Gallifreyans. Apparently the ability, once latent in Susan, had surfaced.
"You caught me," the Doctor said with a dip of his head. "I was just looking for an old friend and I was told he might be here."
"You mean grandfather? The Doctor that is. No, he's never returned," Susan replied with tight lips. "Who are you anyways? Last I checked Grandfather didn't get along with many Time Lords; certainly not those old enough to have already regenerated 10 times."
The Doctor grimaced as the idea of the other-Doctor popped into his head. He didn't like thinking about that man who was not him, and especially wished Susan of all people hadn't brought it up.
The Doctor doesn't know what exactly happened to his granddaughter. He liked to think that she stayed on Earth away from the Time War and lived a nice happy life. He didn't believe it though. Every Gallifreyan was called back to fight on Gallifrey. No one, not even Susan who'd fled Gallifrey at an age that by Time Lord standard was infancy, could escape the draft. Susan, who'd spent her life rebuilding after Dalek destruction, was killed by a Dalek.
Or she was killed by you in the fall of Arcadia. The voice said in the back of his mind causing the Doctor's scowl to grow.
"Are you regenerating now?" Susan asked stepping away.
"Yes, I guess I am aren't I Susan. You're quite right to get away from me. I should probably go before I destroy what you've been sent to build."
Maybe it was the Doctor's words, or maybe it was just the unchanging look in his eyes, but Susan whispered softly, "Grandfather?"
The Doctor nodded. "I know. I look a bit different, but it's been a bit more than 10 years for me."
"Are you here to bring me back to Gallifrey? To fight in the war."
The Doctor almost bit his tongue off. No! Susan couldn't have received the call in this time period. She had so much longer to live! Children to raise.
"Susan listen to me. Don't go back to Gallifrey. I don't care what you have to do, build a TARDIS and hide if you must. Whatever you do don't go back to Gallifrey to fight in the Time War. Please."
"You've already been through it, haven't you grandfather? And it doesn't end well for our people."
"I can't," the Doctor told her tears welling up in his eyes. "I can't tell you. Just promise me Susan that you won't go back to Gallifrey no matter what."
"Of course Grandfather. I promise not to go back to Gallifrey." Eyes wet with tears the Doctor said adieu to his granddaughter for the last time hoping she would be fine.
What the Doctor didn't know as he took off in the TARDIS to find his Rose was that another TARDIS happened to be landing in Susan's yard. She'd been drafted, and she would fight in Arcadia on that last day.
She would live however, like all the Time Lords, and when they awoke from the time lock Susan would know that her grandfather was the reason Gallifrey falls no more.