As he dropped his jacket and started unzipping his fly, Clark Kent realised that this was not his usual phone booth…
For one thing, it was considerably bigger than normal, and the smell of the air was far better. For another, he wasn't alone. The gaunt, grey-haired man watching him intensely from the staircase kind of gave the game away on that score.
"Can I help you, son?" the man asked.
To be fair, this was a bit unusual for the Doctor as well. He wasn't really used to strangers bursting into the Tardis, let alone stripping their clothes off. The last time that happened, the drunk who urinated in the corner before heading back out to the Glasgow streets probably wouldn't remember enough to cause any issues with temporal security.
Clark quickly zipped his fly. How to explain?
"I'm….."
"Yeah, yeah" said the Doctor. "You're on your way to a costume party and needed somewhere a little… authentic, to change into your Superman suit."
Clark hesitated. That actually sounded far better than he would have made up.
"You're right. Is there somewhere I can…"
A light started flashing brightly on the Tardis console, and a high, keening beep filled the space. The Doctor walked over and flicked a switch, to kill the alarm. A second later, he turned from the console screen and stared directly into Clark's eyes.
"Don't you lie to me, laddie. That's no party suit you're got on, is it?"
A look of exposed surprise flashed across Clark's face. Noticing this, the Doctor ploughed on.
"Your name is Clark Kent. You are a reporter for the Daily Planet. And you were born in Smallville, Kansas. Your parents are Jonathan and Martha Kent. Only they aren't, and you're not. Your actual name is Kal-El, you were born on the former planet Krypton to eminent scientist Jor-El, and your actual job is saving the inhabitants of this planet from themselves and from those who would cause them harm."
For the first time in his life, Clark had nothing to say. The Doctor walked over to him and - rather theatrically – reached out and lifted Clark's jaw closed.
"Some things you just can't hide, even behind a pair of rather unflattering spectacles and a sensible haircut."
Clark found his voice.
"Can I ask your name?"
He was greeted with a Cheshire-cat like smile.
"I'm the Doctor"
"Who….?"
"No – just the Doctor" came the response. The Doctor turned away, and couldn't resist a little chuckle and a personal fist-pump at his ability to use his oldest – and favourite – joke. He turned back to face Clark.
"So tell me, Kal-El, What's so important this time that you need to change clothes so publically?"
Clark suddenly remembered.
"The fire! The building…"
He began tearing at his clothes again, not caring that he was being scrutinised by the strange man. He seemed to know everything about him, so there was no point in hiding now.
"Calm down! There's no hurry…"
"But, the people…" stammered Clark.
"One of the things you need to know about me" replied the Doctor, with a wink, "is that with me, time is – well, relative. It really doesn't matter, you'll get there with plenty to spare. You see, you and I – we're… well, we're both in the same line of work."
The Doctor motioned Clark to sit, and (in a way that circumvents all accepted narrative methodology) explained the universe and the role of a Time Lord within it.
"So let me get this straight" said Clark, after ten minutes of science, history, and no little massacre of grammar, "you're a time traveller, this is your ship, it takes you wherever, and whenever, you want, and that's all fine somehow, because it's only you that can do this?"
The Doctor shrugged.
"Well, apart from the bit about me always going where I want, that's pretty much it. And no, you can't write about this." Superhero or no superhero, he's still a reporter, thought the Doctor.
"What about temporal paradoxes? I thought that changing the past had huge consequences?"
The Doctor was impressed. Straight to temporal paradoxes, eh? Smart guy…
"Remember at the beginning, when I said that time was relative? Well, this whole 'temporal paradox' stuff isn't how people – normal everyday people – think it is."
Clark furrowed his brow.
"So, it's perfectly OK to kill a butterfly in China and not expect earthquakes in San Francisco?"
Well, maybe not that smart…
"Not quite" replied the Doctor. "You see, stuff happens. Every day, on every single inhabited planet, stuff happens. All the time. So the future is like some huge great…. well, wibbly thing. It could be changing all the time, but all we know for sure is what now looks like today. So if something happens differently in ancient Rome, for example, or Victorian London, by the time you get to now, the thing I did differently has already happened, and everything appears right. So the actual net effect is as close to zero discernible future changes as makes no difference."
"So…." said Clark cautiously, "you could take me back to Krypton, before it exploded? Just hypothetically, of course?"
"Hypothetically?" mused the Doctor. "Well yes, hypothetically I could, but think of the cost. You've been here, what, about thirty years? How many people's lives have you saved in that time?"
"But I thought you said…"
"If you go back home, have a chat with your dad, decide to stay – or leave ahead of time with him – or even then come back here, you have no way of knowing how things will have changed. the people you saved would still get into peril, and you wouldn't be there to save them. They'd all be dead. The only difference is, you wouldn't know anything about it, because you would be Kal-El somewhere in the universe, and Clark Kent… and Superman… would never have existed."
A look of understanding slowly crept across Clark's face. Noticing this, the Doctor walked over and put his hand on Clark's shoulder.
"That, my boy, is what temporal paradox really means. It's knowing you could do something, and also knowing why you won't…"
The Doctor gave a slight, resigned shrug, and turned towards the console.
"That's how it is, and that's why I can't stop what I do. Same with you. And why the past – our pasts – have to stay right where they are."
The Doctor turned a dial or two, and tapped a button.
"Go get changed, I'll take us back twenty minutes, that should give you plenty of time to save the people in that building. Only…"
"Yes?"
"If you get there a little early and see yourself, please do me a favour and hide behind a tree or something?"