Disclaimer: Characters and situtions owned by the BBC.
Timeline: during the seventy plus years the Doctor spends guarding the vault on Earth, told in a non-linear fashion.
Spoilers: anything up to and including the tenth New Who season is game; ditto for the first two seasons of Torchwood and The Sarah Jane Adventures. Vague spoilers for Evelyn Smythe's storyline in the Big Finish audios.
Thanks to: Kathyh for beta'ing with her usual love and care.
Signs on the slow path
Bristol hadn't been the Doctor's first choice as the place to guard the vault containing Missy, or even the second. But his idea of simply placing the vault in the TARDIS was soundly rejected by the Keepers of the Fatality Index , who insisted it had to be a planet, not a ship. While he briefly toyed with the idea of settling down in the Eye of Orion, he knew that if he did that, he'd never be able to use it as a vacation spot again. Not to mention the fact he was bound to run into other versions of himself there.
"Nonsense," Missy commented, when he talked about the options for what could euphemistically be deemed a shared exile. "Eye of Orion indeed. You 'd be bored to death there, that's why you didn't seriously consider it." Her eyes glittered. "It's going to be Earth, isn't it? The twentieth century, of course. Bloody enough for you to feel heroic about staying there. And not get bored."
He didn't bother refuting what she said. The Master had always been able to simultaneously see all the Doctor wanted to hide and yet miss so much about him, which ensured they'd never run out of ways to surprise each other, not in all those centuries. Well, it would soon be put to the test, wouldn't it?
"Trust you to miss the most important reason," he replied offhandedly. "They don't have electric guitars and amplifiers as good in any other century."
Evelyn had taught at Sheffield Hallam University; even so many years later, he still recalled tracking her down there in pursuit of an anomaly. He'd parted from her in two regenerations and didn't intend to say goodbye for a third time. Instead, he indulged himself by saying hello. Being an accredited lecturer at St. Luke's University meant he got to participate in conferences, if he so chose.
"Dr. Smythe," he said, spotting her in her cardigan almost instantly, "I'm sorry, but I've read your paper on Catherine Willoughby as a possible co-author of Lamentations of a Sinner, and that's hogwash."
She was as indignant as he'd known she would be. They were still arguing in the university canteen by the time everyone else had gone to catch their respective trains, and he hadn't felt that happy for years. At last, she looked at her watch, and looked crestfallen. "Oh. Oh my."
As the Doctor had once been attuned to the various stages of Evelyn Smythe's distress, an uncomfortable suspicion dawned, awoken by the way she pressed her lips together: she wasn't just annoyed about having missed the bus. "Can I give you a lift?" the Doctor asked.
She shook her head. "That would make things worse," she muttered. Her fingers tapped on the table between them, and he realised what the golden ring on it signified. This was before the end of her first marriage. It was only then that the Doctor recalled what Evelyn had once told him: that this first marriage had ended over her attending a conference on her wedding anniversary.
Her older self would undoubtedly have made an extremely scathing comment at this point.
The Doctor felt guilty, though not unambigously so; clearly, the man never deserved Evelyn in the first place, and in any event, years of adventure with his sixth regeneration followed by marriage to the infinitely worthier Rossiter and yet more years of exploration and adventure were awaiting. But then, so were terrible tragedies and heartbreak, and he'd just contributed to making the first of these happen.
"I don't think I'm ready to go home just yet," she said, evidently having made the decision. "Now, you really need to let go of your John Day theory, because..."
It was a perfect day, culminating in him introducing her to her own favourite chocolate cake, which he'd painstakingly prepared in the TARDIS, following her old recipe. Nardole had been both amused and appalled.
She loved the cake. But she was as sharp as she'd ever been, and didn't buy his pretense that it had been made at the canteen for a minute.
"You're a liar," she said, and he didn't see her again.
Nardole wasn't too keen on the twentieth century at first; he was lobbying for the thirtythird. Quite when the Doctor decided on spending his years guarding the vault with Nardole, he couldn't recall. "That's because you didn't," Nardole said. "Your wife did. When she appointed me your guardian. With a special license for kicking your ass, if necessary."
Which was such a River thing to do. Nardole had been with them on Darillium. River would never admit it, she wasn't the type, but she knew very well Nardole's condition as a head on a shared body was her responsibility,and it hadn't taken more than a look on her part, complete with a challenge regarding his mechanical skills, to make the Doctor create a new body for Nardole to possess, as close to his original one as it was possible to get.
"And that's why I can't leave," Nardole said. "I need you around for maintenance."
Or maybe River had known, none better, how he could be when alone for longer than a short time and wanted to save the universe from that.
"Look," the Doctor said, "I'll introduce you to Belgian chocolates. They don't make them anymore after the twenty second century, it's one of the great devastations of the Time War, but trust me on this, their mere existence justifies this century as a starting point."
Nardole liked Belgian chocolates, but what he liked even better was listening to the Goon Show on the radio, so that was alright then.
Ashildr tracked the Doctor down a few years after he'd settled down in Bristol, though they met at a village fete in Sussex. He didn't know why he still thought of her as Ashildr; she'd made it clear she was Me now. Maybe because being called Me was what she preferred, and he remembered an all consuming rage directed at her, which needed to vent in such petty channels.
It was odd, remembering such a powerful emotion without actually feeling it. Intellectually, he knew that Ashildr had something to do with him losing Clara and remaining trapped in his confession dial for billions of subjective years. But as with everything else connected to Clara beyond the fact that she'd existed, the details were gone along with the emotions. On the other hand, he could recall his second encounter with Ashildr precisely, which meant Clara could not have been present, and he knew it had ended with Ashildr vowing to protect the Earth from him. Perhaps that had been what she was doing, would do, in the future. He simply could not tell.
"What are you doing here, Doctor?" the present version of her asked, a version who had not yet done whatever it was, because she was linear, taking the slow path, a fate which he had created for her, which he could not forget for a moment.
"Speaking baby, of course," he retorted as lightheartedly as he could. It wasn't a lie. He was sitting next to a pram with a baby inside, a baby born only this year, a baby whose parents had just driven off to meet their fate on a country road.
It was 1951, and Sarah Jane Smith would not see her parents again. At least not for decades to come. She'd told him about it after it happened, time breaking apart and resetting again, courtesy of her enemy the Trickster. The Doctor could not interfere in this, and he'd waited to make his appearance here until adult Sarah as well as Luke and Rani had left. But here was baby Sarah Jane, condemned to days of confusion and despair until her aunt Lavinia came to retrieve her, and he was damned if he would let that happen.
He listened to the baby version of Sarah tell him all about the noises and the water from the sky that was now gone, listened to her demands for her mother and explained, as best he could. It came handy, having two heartbeats, if you needed a baby to focus on something other than the absence of its mother's warmth while cradling it.
"You're not here to play nanny, Doctor," Ashildr said, her scepticism written all over her eternally youthful features.
"But I am," he said. "For two days more."
Ashildr looked at tiny Sarah, and something rippled through her face. She'd had children, he recalled, and she'd seen them die, but she only knew about this now because she'd kept those pages from her diaries as a warning to herself. The memories themselves, and the emotions tied to them were gone from her human, still human mind. He hadn't truly understood how that would feel until waking up and knowing there'd been someone named Clara in his life, but that whatever she'd meant had been erased.
Silently, Ashildr sat down next to him and watched him soothe baby Sarah into sleep. "Two days, then," she eventually said. "And you know I'll keep an eye on this baby from now on."
Missy remembered Clara, of course. "Short, bossy, freakishly large eyes," she said. "Adored me."
"That's not true."
She tsked. "Is, too. Those eyes were Disney sized."
"You've hated every single one of my friends since we left the Academy," the Doctor said. He'd brought her Melgavian apples, freshly fried, courtesy of a five minutes trip with the TARDIS Nardole thankfully did not notice. "You've also tried to kill them on a regular basis. It doesn't tend to produce adoration."
Missy used her nails to expertly slice an apple. "Firstly," she said, "I didn't hate all of them. I found Miss Grant quite tolerable, eventually. And secondly, you've let me burn alive, and I adore you, so frankly, I think I'm entitled to my own opinion as to which feelings aren't mutually exclusive."
He forebore to mention that she'd tried to kill him a great deal more often, and when it came to torture, mental and physical, she was so far ahead that it wasn't even up for discussion. Instead, he took the bit of apple she was handing over to him and ate it whole.
It had occurred to him to contact Jack as soon as he'd arrived for his millennium long vigil, of course, but Jack Harkness was a fixed point in time, and Jack had been very clear about not having encountered the Doctor past his ninth regeneration again until 2007 in Cardiff. At least the version of Jack who had been left stranded on a satellite had not. Jack at a later point in his timeline was another matter.
When the Doctor dug Jack out of the ground in the year 27 AD after Jack had been buried there by his younger brother and John Hart, Jack was less than grateful once he discovered that he wasn't about to be returned to Cardiff in time to prevent his brother from wrecking further mayhem.
"You'll get there eventually," the Doctor promised. "After being discovered by the Torchwood team of 1901 who'll store you in cryosleep until 2008. This has already happened, so I'm afraid there's no way around it. But there's no reason for you to spend so many centuries in the ground in between."
Dying and reviving again and again, he didn't add. After the confession dial, he had a new perspective on this particular torment. There was so much pain in the life of Jack Harkness, past, present and future, which the Doctor couldn't do anything about without destroying the web of time, but this one thing he could change.
"If you say so," Jack commented doubtfully. Then his brow cleared. "Well, there's no need to rebury me in 1901 right away, is there? I'd be fine with running along with you for a while now, Doctor. As long as you swear I'll be in Cardiff in time afterwards. " Unbelievably, he produced a version of his come hither smile. "Admit it, you missed me."
Some things about Jack Harkness remained constant, and that fact provided the Doctor with a great deal of comfort and inspiration on most days. Though not right now, because he knew what was coming. But he couldn't lie to Jack. Not about this.
"I'm afraid my running days are over right now, Jack", he replied carefully. "I can do the occasional five minute interlude in an emergency, sure, but by and large, I have to take the slow path. I made a promise."
Jack looked surprised more than anything else, and whistled, sounding impressed. "Given how you hate standing still, it has to be about protecting the innocent from something incredibly dangerous, or true love. So which is it, Doctor?"
The Doctor didn't reply, and the expression of mixed amusement and respect faded from Jack's features. You could tell the moment he understood, because of course he did. He'd been present on the Valiant the first time the Doctor made the offer, after all.
"No," Jack said disgustedly. "You never learn, do you? Care to bet how many of us that bastard will murder this time to get his jollies?"
Jack had endured an entire year of torture at the Master's hands. He was more than entitled to ask that question.
"None," the Doctor said, hoping with all he had that he was speaking the truth. "Because I intend to keep that promise."
Jack turned away. "Better bring me to 1901 then," he said. "I have to return to stop my own homicidal maniac. Because I put the lives of my friends first."
The Doctor hadn't entirely been kidding about the guitars. In 1946, he spent a blissful day and night with Les Paul, assisting him in his model building in order to convince Gibson to go into serial production. When Maurice Berlin, still heading Gibson at that point, declined, a depressed Les let him have one of the rejected models.
"I suppose if St. Lukes fires you in a decade or three we can always sell it," Nardole said. "Because some of us would like to have actual money now and then on a planet where the economy still relies on it."
"Blasphemy", the Doctor replied, stroking "the log", as the model was nicknamed.
Ace at age 13 was a tiny ball of rage cocooned in misery and snot. She had just spent an hour at the police station being interrogated about the fire she'd set to the mansion Gabriel Chase. On the way out of the station, her mother was still berating her while occasionally glancing at the tall gentleman with the Scottish accent who'd turned up to be their pro bono lawyer. It was one of the Doctor's more successful impersonations. The psychic paper really came in handy sometimes.
"You're so lucky they let you go, miss," Audrey McShane hissed. "I know you did it."
"They should be going after the Nazis who firebombed Manisha's flat", Ace said contempteously. "Manisha died. But her flat wasn't a stupid posh mansion, so they don't. Stupid pigs!"
Her mother raised her arm to slap her, and the Doctor harrumphed. Audrey's arm sank down. It was embarrassment and exhaustion more than anything else that held her back, the Doctor thought; Ace at that age was arguing with her mother on a daily basis, but usually not in front of strangers.
"I don't think," the Doctor said, "that there'll be any more investigations. Of either fire, sadly."
"Pigs," Ace repeated. There was grief behind the sullenness, terrible grief; but even at this age, Ace found it easier to be angry than admit to mourning or fear.
"I've had it with you", her mother said numbly. "You do what you want, Dorothy. Light another fire, join a terrorist organisation, why don't you. The Purkayashtas had invited us to the funeral, you know, but no, you had to torch down some building instead, and now you can't even say goodbye to your friend. It's your own goddamn fault."
Ace refused to follow her any further, but Audrey kept going, until she'd disappeared around the corner.
"Why are you still here?" Ace asked the Doctor, full of distrust. Her voice was tightly compressed.
He'd heard that tone from her quite often, in the final days before she left for good. Of course, there were countless better memories to draw from - her voice full of joy, bravery, wonder - and just to see her was happiness and heartbreak at the same time. He was tempted to do some cheap magic tricks to cheer her up right now, but she'd put two and two together later if he did that, smart as she was.
Because, the Doctor thought, because I'm sorry about your friend. I'm sorry about your mother. I'm sorry for putting you through all that again years later. I'm not sorry for letting you travel with me far longer than any human being should, I'm not sorry for making you a Time Lord, because, Ace, you became a better one than anyone born on Gallifrey.
"Two reasons," the Doctor said instead. "Firstly, I am a ruthless capitalist lawyer set on exploiting 1980s youth culture. And secondly, you, Ace McShane, are a target of a marketing campaign of rock star merchandise, which is why I have a ticket for a David Bowie concert for you."
She stared at him, her face scrunched up in disbelief.
"Ace?" she repeated, and he could have slapped himself. Stupid, stupid Doctor. Of course her mother and the police had only referred to her as Dorothy in his hearing. He was reasonably certain she'd already begun calling herself Ace at this point, but the man he pretended to be had no way of knowing that. Ace, burning so very, very brightly.
When found out, denial was best. He didn't even attempt an explanation. Instead, he just produced the ticket, holding it out to her, and tried very hard to conjure up his most enigmatic expression. But that one had always suited his seventh regeneration far better.
"Unless Bowie is too old for you," the Doctor said, sounding lamely even to himself.
"Eh. He's no Johnny Chess, but he's alright, I suppose," Ace said, still scowling, and took the ticket.
The Doctor had expected escape attempts from Missy, and was in fact counting on them, because foiling her would provide an intellectual challenge. He'd also expected her to abandon her pretense of acceptance soon in favour of anger and an endless delight in needling and goading him, and sure enough, she produced all of this, and he was prepared for it. But what he hadn't expected was how he'd feel when he found her sunk in lethargy and depression. To see her drained of all her vitality, brilliance and vicious glee was almost as bad as watching her die.
"You made a far better human than I did, you know", he told her, both because it was true and because he knew it would enrage her .
Her hair was frizzled and oily at the same time, despite the fact the vault used transdimensional technology and provided her with baths and showers at her leisure. When his body wasn't radically decaying, the Master in all his regenerations had always been vain about his appearance, so this by itself was alarming.
"You're making even less sense than usual," she retorted, which was pathetic by her standards.
"But you did. Yana was a lovely man. Kind, brilliant, dedicated to saving his people. Meanwhile, I was a rubbish teacher at some posh school that made the Academy on Gallifrey look progressive, and just managed to ruin a woman's life. Face it, you have an inner philanthropist and hero just waiting to emerge."
Her eyes narrowed. "Crushing on Yana, were we? Well, I've got news for you, Doctor. Nothing about Yana was me. He was a disguise. Paint on the face, no more."
"See, that's where having been human comes in handy. I know better. Wish I didn't, because John Smith was nothing to write home about. But he was me. How I'd have been if I never left Gallifrey. And Yana was you, if you..."
Until then, they'd been sitting on the 1970s water bed he'd organized because he thought it would amuse her. Now she pushed him onto the floor. There was nothing feeble or lethargic about that push.
"If Yana was such a lovely man, such a worthy human, then tell me something, Doctor. Say Martha Jones had figured out what the stopwatch was a bit sooner, say you'd run faster and reached me before I could open the chameleon arch. What would you have done? Would you have kept Yana around, that excellent human being, or would you have let me open the watch just to get one of your people back and get rid of that tiny bit of guilt?"
He'd wondered about that himself, more than once, during that long year when he'd been the Master's prisoner, trapped in a body that was falling apart while the Earth burned beneath them.
"I'd have kept Yana," the Doctor said, "if I'd only known he was a Time Lord in disguise. I'd never have told him the truth, not until it was time for him to die, and then I'd have given him a choice. But if I'd known he was you..." He got up from the floor. He'd started out this day feeling weary and exhausted himself, facing another class of humans who'd be grandparents in less than the blink of an eye. But his own depression was gone now. "I'd have returned Martha and Jack to Earth, and then I'd have gone back to Utopia and let you open it. Always."
"Doctor, Doctor", she sang, "please, oh the mess I'm in..."
And there it was, that spark in her eyes, ready to consume the world.
"So what you're saying is that you've basically opened a travel agency behind my back?" the Doctor demanded.
Theoretically, he'd been aware that Nardole had hours at his disposal which weren't filled by organizing the Doctor's schedule at St. Luke's or helping him foil the occasional invasion that hadn't already been foiled by other versions of himself. In practice, finding him handing over an "Earth in 1967: a how to guide" to a couple of Trakenites was something of a surprise.
Nardole shrugged. "Look, not every visitor here comes with an evil plot, you've said it yourself. Many are just tourists. I thought, if it were me, I'd be grateful for tips."
"As long as you're keeping them away from the Himalayas", the Doctor said distractedly, studying the tablet. "That's where I wanted... hang on. No. No, no, no. This won't do!"
The Trakenite couple looked at each other, then at Nardole and the Doctor, who was incensed enough that their appearance didn't remind him of Nyssa, or the way the Master had kidnapped the body of Nyssa's father, and worriedly wanted to know what was wrong.
"Forget the Monterey Pop Festival in June," the Doctor declared. "If you really want to sample Earth's musical culture at its finest, you have to go to the Saville Theatre in July. Jimi Hendrix opens with Sgt. Pepper's Lonely Hearts Club Band just three days after the Beatles release the album. That's the gig to listen to!"
Quite how this ended in him and Nardole accompagnying the Trakenites to the Saville, he didn't know, but judging by Nardole's somewhat smug expression, the Doctor suspected he might have been set up.
Still, it was worth it. Even if he had to avoid his previous self, Jack and Rose attending the concert.
Some of the Doctor's likes and dislikes varied from regeneration to regeneration. But through all his lives so far, he'd loathed bus stations. Terrible places, he'd once told Ace, full of lost luggage and lost souls. He didn't like them any more while visiting one during one particular week in the 1970s, a summer week, with enough people coming and going to mask those like him. The ones who stayed, sitting around through most of the day and into the night. And yet he remained, for this was the right week, he knew it, and the part of his soul he was waiting for would come here.
In the meantime, he brushed up his juggling act and learned all about Hettie the homeless woman whose territory this bus station was, and who said she'd met him before, though she didn't know where or when. In between organizing ice cream for her and the other regulars he caught up with Nardole on the phone, but terms were over at St. Luke's, and the vault remained unchanged.
On the sixth day, the Doctor spotted the person he was waiting for; six years old, red hair bound back in a pony-tail, her hand clutching a twenty pound note. "And where's your mum and dad, love?" the bus driver asked when she entered the National Express coach.
"They're already in Scotland," she replied, voice not even wavering. Were it not for the wave of guilt which reliably engulfed the Doctor when he saw her, he'd have been amused; she'd always been a good liar if she wanted to be. "It's our holiday trip. But I had the measles, so I'm late."
"And your father and mother went ahead when you were sick?" the bus driver asked, deeply sceptical. The Doctor decided this was as good a moment to intervene as any. He entered the coach as well.
"Donna! There you are. I've been looking all over for you."
"And you are...?" asked the bus driver, wavering between the relief of spotting a responsible adult and retaining quite justified distrust.
"A friend of her grandfather's," the Doctor said firmly. "Wilf told me to take her to Strathclyde. I live there."
His accent fit the story, and he added a few details, said he was an astronomer friend of Wilf's, a pen pal, and since there were more passengers lining up behind him by now, the bus driver abandoned his remaining doubts and waved them inside.
When they sat down next to each other, Donna crossed her arms and observed him critically. "Are you an axe murderer? Mum says they're always looking for children. Or are you the tooth fairy?"
"My teeth aren't that bad," the Doctor protested. "And I haven't killed anyone with an axe yet. How does one qualify as an axe murderer anyway? Does it have to be one of those axes they cut wood with? Or maybe one of those hatchets, what are they called, the tiny ones smiths use for jewelry? Because then I'm not so sure. I'm a Smith, after all."
"Well, you're a liar," she stated. "Because Gramps doesn't know I'm running away. I haven't told him."
"Grandfathers know everything. Just out of curiosity, though, if you think I'm an axe murderer, why didn't you say something to the bus driver?"
"Because maybe you're not," Donna Noble, age six, said. "And if you are, I can scream really loudly. No one else can scream that loud! So if you are, and can't travel with me, and you go to some other bus and kill someone else, they can't scream like I can." She frowned. "Also, I really want to go to Scotland. Mum had promised, and then she wouldn't take me, just because they sent me home from school for biting."
"I see your point", the Doctor said, swallowing down the guilt along with the tears. This was for her. It would be a good memory for her. One that she kept. "Well, if I were a murderer, then I'd better be postponing my plans. Since I don't want to be bitten. Or yelled at."
"You could bite back," she said generously. "Your teeth are really long."
"That's why I always polish them with jelly beans," he told her and produced some. She watched him eat them first before accepting some herself, but then she told him about school, and how unfair it was. By the time the bus took its first longer break, he'd gone through his repertoire of coins, flowers and bits and pieces of stars which he found behind her ears or shook out of her sleeves, and she was asking for stories about Scotland. She preferred the ones starring Jamie McCrimmon to the one of the Loch Ness Monster. When they were arriving in Glasgow, it was night, and she'd fallen asleep. Her head was resting on his shoulder.
Wilf as well as Geoffrey Noble would be waiting at the central station, the Doctor knew. Wilf really had told him all about that time Donna had taken the bus and gone as far as Strathoclyde.
Years and years from now, in the future which was the past and always would be. A fixed point in time.
"Donna," the Doctor murmured, but she truly was asleep, and didn't notice when he carefully withdrew. By the time the bus had emptied enough for her anxious father and grandfather to enter, he was gone.
"Not to critisize," Nardole said at some point during the nineties, when life at the university seemed to consist of endless budget fights and upholding office hours was a struggle worse than having it out with the Daleks, which meant the Doctor was in a terrible mood and Missy was worse, "but wouldn't it be easier for you and Mistress Evil down there if you just put her into cryosleep, bury her somewhere and build yourself a library on top of it for the remaining ninehundred plus years? You can still defrost her afterwards if you absolutely must."
"That's missing the point."
The Doctor, who'd been repairing a crack in the support hangers of the Clifton Suspension Bridge which was just his excuse for trying out bungee jumping afterwards, barely looked up when he replied: "Change. I have to believe she and I can change."
It was 1963, and Ian Chesterton led a school field trip to the Greenwich Observatory. It was also the only point in time where the Doctor could be sure his earliest self would not be anywhere near Susan, and nor would Barbara, who'd always been far too sharp eyed and observant not to notice a strange man showing an undue interest in one of her teenage students, and who'd have had no compunction about dealing with said strange man. With a certain nostalgia, the Doctor recalled her blistering summation of his character flaws only weeks after their first encounter, at a point when he'd been her only hope of ever returning to her present again.
Chesterton, now, Chesterton also was protective of his students, of course, but it was a warm September day, and he was thinking of the lovely history teacher who wasn't with him, so he kept an eye on the unrulier members of the class mingling with tourists on the upper deck of one of the Thames boats on its way to Greenwich but missed out on Susan Foreman, who was leaning on the railing while watching the changing riverside and mentally comparing it with the last time she'd seen it, hidden on one of Henry VIII.'s barges with her grandfather. He didn't notice anything unusual in the grey-haired gentleman joining her at the railing.
The Doctor was still incredibly fond of Ian Chesterton, but he wasn't feeling very repentant for some of the jibes his younger self would soon send Ian's way.
Hard to notice anything about Ian at all, though, at this moment, because here she was. Before the return of Gallifrey, even in a hidden way, he would not have been able to approach her at any point in time, not after the Time War. But that was changed now. Gallifrey Falls No More. All changed, changed utterly. The last time he'd seen her, she'd been standing behind Rassilon, grieving, muted, but desperately staring at him and telling him in her thoughts what to do. And he'd shot at the White Point Star, sending all Time Lords, including her, back to the hell of the Time War. Now here she was, young, so very young, not because she looked like a teenager but because her entire life was still ahead of her.
"I think I got a bit sick on Henry's barge," he said to her, speaking not English, but Gallifreyan, and though the TARDIS translation circuits were attuned to both of them, she noticed at once. Of course she did. "But it was a good day."
He kept his voice casual. It was that, or sobbing all over the place, and both his earliest and his current self abhorred that kind of behaviour when it came to themselves.
The smile with which she'd greeted him turned quizzical, and then her eyes widened, and she understood.
"But - when? I should have been there!" she exclaimed, sounding distressed, and he hastily clarified he hadn't regenerated now, nor would he, not for a good long while. It was just that he was in the area and couldn't resist dropping by, which she was not to mention at home, lest the time stream be polluted and crossed.
She nodded and promised, though there was mischief dancing in her dark eyes as she added: "The TARDIS still does what she wants with you, admit it, Grandfather. You're lost again. That's why you're here!"
He was convinced, then, that he'd have the strength to stay, not just through this century but the following one, right until the invasion of the Daleks and her life with David Campbell in the aftermath.
"Yes," the Doctor said. "Susan, my dear. That is why I am back."