1) The TARDIS
They aren't the last two of their kind – yet – but they need each other to survive. The old-looking young man and the living machine: the former unsuited for a life of tedious non-intervention, the latter discarded in favour of newer and shinier toys.
The Doctor pounds hard and inexpertly on the controls to bend her to his will, but eventually she complies; after all, a fugitive's life is better than none. Hundreds of years will pass as man and machine bicker, commiserate, laugh, kiss and make up, as married as any couple.
It's symbiosis, or maybe love at first sight.
The Doctor is still relatively new to this body when he meets the young Scotsman and his fellow soldiers. Jamie is brave, brash, and loyal, some of the Doctor's favourite human characteristics, but in the midst of battle, there's no time to waste on foolish attractions.
He's had many friends since he came to this world, and Jamie will just be another, he tells himself. A hand on his companion's shoulder is merely reassurance of his presence; a light touch, a lingering glance, are protectiveness, surely not something more.
How strange, how delightful, to find that Jamie's thought the same.
The lateral molecular rectifier would fix everything, he tells Liz, if only he could fetch it from his locked TARDIS. Though she's suspicious (rightly so, clever girl), she nicks the key for him anyway.
After his futile, chastening escape attempt, there's nothing for it but to throw himself into his work with Liz. Analysis, experimentation, investigation, saving the Earth – all the more exhilarating when shared with someone who loves science and mystery as much as he does. (Her short skirts are a pleasant distraction as well.)
There's no substitute for freedom, but captivity, it seems, has its own advantages.
4) Romana I/II
Life is fine, better than fine, just him and K-9 tramping cheerfully about the universe, when Romana gets dumped in his lap.
He resents her intelligence, her youthful arrogance, her unavoidable reminder of the world he abandoned, but there's no choice but to travel with her.
She learns to appreciate his recklessness. He learns to appreciate her cool confidence. And atop the Eiffel Tower, introducing Romana to Paris and its bouquet, the Doctor realises he's fallen in love.
She outgrows him – they all do – but he carries her in his hearts still.
Because she is Romana, and she's superb.
She's unquestionably the most infuriating woman he's ever met, with her constant complaints, whines, and insults. Each day he considers dumping her on some out-of-the-way planetoid; each night her nails claw his back, her whines become screams of "more, faster, now, please," and he knows he couldn't let go if he tried.
He never intended to take her for a lover, and she's always half-in, half-out of his bed, longing for the normalcy of home yet unwilling to give him up. They orbit like moons bound by each other's gravity, unable to escape until a violent event drives them apart.
This regeneration's gone all wrong. It isn't Peri's fault – he's risked his life to save a human's many times, and this likely isn't the only time he'll die for one – but the spectrox has left him off-balance, even violent. Best to distance himself from Peri, keep her safe.
She makes it easier with question after irritating question. What's the point of fishing? Can't we go somewhere else? Leading him to another: Is she worth the trouble?
When he discovers her death's only a trick, he has his answer. So relieved she's alive, and happy, and far from him.
"Ace, you're not carrying any nitro-9, are you?" he asks.
"No, Professor," Ace replies. The Doctor knows she's lying, and knows Ace is equally aware of his knowledge, but this mutual deception is an unspoken ritual they share: Ace pretends she'll try to domesticate herself, and the Doctor pretends he doesn't need her to stay undomesticated.
As deceptions go for him, it's tame. He guides Ace with schemes and incomplete truths, manoeuvring her along the path he's set, a faithful parent steering his wayward, wilful child.
Is this how fathers should behave? After so many years, he no longer remembers.
8) Romana II (again)
The Doctor knows it's only a matter of hours before the Daleks complete their assault on Gallifrey, yet he's lying in bed with Romana.
They should be fighting – neither is accustomed to surrender – but this close to the end, selfishness overpowers patriotism. Besides, the Doctor's mission will be sacrifice enough for both.
They twine together, sharing kisses and whispered secrets and reminiscences, until at last Romana orders him to go.
Later, as he lies crushed and bleeding in the TARDIS, he wonders whether dying, finally dying, will feel different from all the other times.
He loves Romana anyway.
They had barely an hour together, so his memories of her are few and precious: the cedar scent of her skin, the cool breeze of absolution that wafted through her leaves. She alone recognised him, and in exchange for his friendship she was incinerated, reduced to ashes and charcoal.
Gallifrey, Jabe, the Earth: whatever made him think an afternoon of destruction could serve as entertainment? Are he and death so familiar now?
Fire has claimed enough today, he decides. He kneels outside Rose's room, his palm pressed to the door, hoping he has the strength to protect one tiny human.
Reinette's kiss leaves him shocked, breathless, exhilarated. Just a few seconds long, that magnificent kiss, but sufficient for the voice inside his head chiding but you love Rose to be drowned out by one saying you love them all.
It's even more shocking that Reinette can stroll through his mind so casually. The secrets he conceals have never needed to be locked away from humans, crude emotions their only tool to pry at him. Having one draw open the barred door to his past is unsettling, and yet unspeakably seductive.
When she leads him to the dance, he follows willingly.
"So good to see you, Martha," he chokes out before screaming, exploding in golden sparks to shed the battered husk of his tenth body. He collapses in her arms without warning or apology.
The Doctor awakes on the couch, a cool cloth on his forehead.
"You dropped by to die on my front steps," Martha says. "You're flattering me, right?"
"I knew you'd take care of me."
"How many more times am I going to have to save your life?"
"Hopefully, none. But you're awfully good at it."
Martha sighs, kisses his cheek. "Flattery will get you everywhere, Mr. Smith."
He lands the TARDIS at the playground where Rose is watching her grandchildren shriek and squeal on the roundabout. Rose's face is lined, her hair silver-white, but her smile still makes his hearts leap.
"You're about sixty years late," she says. "For a Time Lord, you always did have rubbish timing."
"I'll have you know I passed transtemporal navigation. Eventually."
"You realise I won't go with you. That part of my life's done and gone."
"Yes," he acknowledges. "But I came anyway. Because I could." He reaches for her hand, and for a few moments, they are in love again.
A hundred years they've travelled together, facing death in its worst forms, and what finally fells him is a venomous creature no bigger than his thumb.
He stops Jack from wasting time dragging him to the TARDIS. "Don't go," Jack pleads. "There's so much left to do."
"We'll meet again," the Doctor croaks, "but you'll have quite a swelled head by then." Breathing feels like swimming through mud, but there's one thing left to say, one creature remaining who needs his protection. "Take care of the old girl. She loves you too."
He closes his eyes, and sleeps at last.