"Well, looks like I do get to see what happens next, after all," is what the Doctor says to herself as she suddenly finds herself standing on the same rocky clifftop overlooking the same ocean where she had earlier begun to shed her current form in blazing regeneration. That she lives does not surprise her; that she has not changed her body does. Once before the Doctor kept the same face upon regenerating, but those were unique circumstances. She...this Doctor...should not still exist, and yet she does. Looking away from the sea, she laughs with delight as she sees the TARDIS right where she left the old girl. "I know where I'm going!" she exclaims as she runs to it.
A block of flats in Sheffield, the thirty-fourth apartment, that's where. The Doctors knocks, the door opens, and she sees the face she has come here to see. "Yaz," she says to the woman who has been her companion, her friend...and maybe something more. Her hearts leap as she continues: I'm not sure how, exactly, I must have regenerated, I must have, but I'm still me, I've not changed, we can still travel together! We can..." Then her voice trails off as she registers how Yasmin Khan, 'Yaz' to her friends, is older than she was when they were last together. Only slightly, but still older. Then she notices the bulge in Yaz's belly. The sign of impending motherhood. Normally, the Doctor would be happy. But...
Yaz smiles, but anyone could sense the sadness mixed with the joy she feels at seeing her friend, this remarkable woman. "Hello, Doctor," she says. "Come in. Let's talk." Yaz's parents are in. They say hello, the Doctor tries to make small talk while Yaz brews the tea in the kitchen; it goes awkwardly. When Yaz brings the tea, she also brings a custard cream biscuit, which the Doctor thinks is a nice touch. Then, slowly and carefully, Yaz explains. How it's been years since she and the Doctor traveled together. Since the day the two of them sat and ate ice creams together on the roof of the TARDIS; since Yaz was dropped off in a park and the Doctor said goodbye. "I've moved on," she says, only half looking at the Doctor. "I've met other people. One person...Simon...We've become very close." She touches her belly. "As you can see. I don't even live here anymore, I'm just visiting my mum and dad. Doctor, I loved you, I loved everything we experienced together. But I can't go back to that life. I've got a new adventure in front of me now. One every bit as magical as what we went through, if not even more so. Can you understand?"
The Doctor's tea and custard cream are untouched. She thinks of all those others across her many lives. Ace, Peri, Tegan, Nyssa, Romana, Leela, Jo, and so many more. All had left,but had found new and great paths to travel. Yaz is one more, and she can't help being glad for this young woman from Sheffield. There's pain, but peace as well. Yaz gives her the address of her and her partner, says she's always welcome to visit.
Nearly two years go by for Earth, for its people, its beauties and horrors. Yaz is in her and her husband's home one afternoon, her daughter asleep upstairs, when the sound of the doorbell drags her away from the book she's reading. Opening the door, she cries out "Doctor!", her smile of delight mirroring that of the woman standing in front of her. Then she sees what the Doctor is holding at her side: A carry-cot, and inside, a small, sleeping baby.
Seeing the shocked confusion on her friend's face, the Doctor announces "Afternoon, Yaz. Mind if I...well, we...come in?" In a few moments the two of them are sitting togetheron the sofa, the Doctor holding her baby in her arms as she and Yaz peer into his resting face. "His name's Ian," the Doctor says softly. "I named him after one of the first humans I traveled with, after I left Gallifrey. Before that it had just been me and Susan, my granddaughter. We'd come to London, and Susan decided she wanted to go to school there. Ian Chesterton was one of her teachers..."
Yaz might have told the Doctor that she knows the man she's talking about, that she met him once at a gathering of others that had been in the TARDIS. But right now she's enraptured by this tiny infant, the very fact of his existence. "He's beautiful, Doctor," she gasps. "But...how did it happen?"
The Doctor sighs slightly, her eyes drifting elsewhere. "Somewhere in the far future, there's a man. A good man who will save his world and people froma terrible threat. But in order for him to do that, I...had to give him something...and this is what he gave me. He doesn't know. Maybe one day, I'll take Ian to see his dad...but not yet. For now, it's just him and me, like it was me and Susan." She looks at Yaz and grins. "Now, you've seen mine. You gonna show me yours?"