He wasn't what she was expecting.

When Liz Shaw had been seconded – or, as she was inclined to think of it, drafted – to UNIT, she had formed a mental image of the man whose name was neatly typed at the bottom of the correspondence. Brigadier A.G. Lethbridge-Stewart, she thought, would doubtless prove to be a short, fat, bald little man in an ill-fitting uniform, who had nothing better to do than sit behind a desk all day shouting orders at hapless subordinates, and wondering whether he would make General before he retired. She loathed him already, even before she stepped out of the car that had brought her from Cambridge to the underground car park beneath St Pancras Station.

Really, the level of security was quite ridiculous, especially since she'd already signed the Official Secrets Act. This man must be paranoid! she thought, as she stepped through one last checkpoint and followed the guard along the corridor towards the door at the end. A tall, good-looking, dark haired officer stood outside it – the Brigadier's adjutant, Liz guessed, probably waiting to usher her inside to meet the man himself.

"Miss Shaw?" he said, as she approached, "I'm Lethbridge-Stewart. Do come in."

Liz shook his hand automatically, too surprised to respond immediately to his introduction. Despite the moustache – and the rows of medal ribbons on his chest – he looked ridiculously young to be a Brigadier. As she sat down, she mentally relabelled him 'ambitious bastard', and launched into the tirade she'd prepared.

"Is all this security really necessary?"

He leafed through her file (where on earth had he got that from? she wondered). He spun her a yarn about impossible meteorites. He made her laugh out loud with claims of alien invasions – though his eyes flashed a very steely blue when she so clearly disbelieved him.

"I'm not in the habit of lying, Miss Shaw."

He really did seem to be sincere, and Liz wondered if this was all part of some strange test. Then the phone on his desk rang and, after a brief conversation that seemed to be about an abandoned police box, he stood up to go.

And somehow, before Liz had time to think about objection or refusal, she had been ushered back outside the building and into the back of a waiting car.

As the car pulled out onto Euston Road, Liz took up her cudgel again. "So. Alien invasions," she said, folding her arms as she settled back against the leather upholstery, "Do tell."

"I'll show you the files when we get back," said the Brigadier, obviously hearing the disbelief in her voice, "But in a nutshell: you remember the nerve gas attack on the London Underground five years ago?"

"Yes, of course. The whole of central London was closed for weeks! Are you saying…?"

"Nerve gas was the cover story," he said, matter-of-factly, "The powers-that-be didn't want to alarm the public by telling them the truth."

"Which was?"

"That an alien entity known as the Great Intelligence had attacked the city, and was using the Tube as its base."

Liz couldn't help but laugh. "Oh, really, Brigadier, what nonsense!"

He turned to glare at her. "I was there, Miss Shaw. Are you going to accuse me of lying again?"

"You don't seem to have any qualms about lying to the Press and the public," she retorted, "Why on earth do you expect me to believe such a ridiculous story?"

"You've signed the Official Secrets Act," he said, his expression straight, his voice sincere, "They haven't."

Liz was beginning to feel that she'd stepped into the pages of Alice in Wonderland – except that there'd been something about the look in the Brigadier's eyes when he'd said that he was there… something that, just for a moment, spoke of horror and loss. She looked out of the window, struggling to reconcile the busy normality of London's outskirts with the incredible tale she had just heard.

"You said there were two attempted invasions?"

He nodded. "Last year there were photos in the papers of silver robots on the steps of St Paul's."

"Brandishing their ray guns," she said, recollecting the story, "As I recall, that was a hoax perpetrated by a bunch of students for their rag week. They were interviewed on television confessing all, if I remember correctly."

"They were interviewed, yes," said the Brigadier, "But they weren't students. They were the youngest UNIT recruits I could find, dressed in civvies and carefully briefed on what to say to the media. That was the hoax. The robots – or cybermen as we call them – were quite real. And very, very deadly."

"So where are we going now?" said Liz, trying to keep the cynicism out of her voice and not succeeding, "All I got from your end of the phone conversation was something about someone being found near a police box. I'd hardly have thought that heralded an alien invasion."

The Brigadier's mouth quirked in amusement. "Not an invasion, no. But if the man they've found is who I think it is – who I hope it might be – then the word 'alien' applies. That scientist I mentioned who helped us out with the Intelligence and the cybermen? He had a sort of time machine that looks like a Police Box. That's why I told my Captain to put a guard on it, and that's why we're going to the hospital to see who it is they've found."

Liz worked it out then, and began to laugh. "Oh, for heaven's sake! This is one of those TV set-ups, isn't it?" she said, looking around for the hidden camera, "Film the Cambridge Professor making a fool of herself, then put it on the telly?" She leaned over the empty front passenger seat and waved at the dashboard. "OK. Joke's over." She sat back and addressed the man playing soldier in the seat next to her. "Who wrote in? One of my students? I'll bet it was Worsley. Just because I marked him down on his last essay, the sneaky little swine. Wait till he takes his Finals!" She shook her head, annoyed with herself that it had taken her so long to figure it out. "I should have known from the get-go," she said, "I mean, that isn't even a real army uniform, is it? And you're good – I mean you really had me going for a while there - but you're much too young to be a Brigadier."

He looked vastly amused. Liz gave him a re-appraising once-over and decided that now she could get past the uniform he was really quite fanciable. Perhaps they could go for a drink later, once this farce had played itself out?

There was a chuckle from the front seat, and she saw the driver was grinning as he glanced in the mirror. "Will you tell her, sir, or shall I?"

"She'll find out soon enough, Norton," came the reply, "When we get to the hospital."

An hour or so later, Liz was back in the car. She sat in the front passenger seat and put her face in her hands. "It's real, isn't it?" she said, cringing as she remembered what she'd said about the uniforms. Not to mention the Brigadier. When she'd seen the cameras inside, her first thought was that she'd been right. But she'd quickly realised that there were just too many of them – there were too many soldiers saluting, too many cameras, too many reporters – and their attention had all been on the Brigadier. They hadn't taken any interest in her at all, probably hadn't even noticed her.

"It's real, miss," said the driver, sympathy in his voice, "But if it's any consolation, I didn't believe in alien invaders either, till I came up against the cybermen. I thought the whole UNIT thing was just a cover for funny stuff – you know, MI5 and that."

Liz took a deep breath and sat back. "That's a better theory than the one I came up with," she said.

He gave her a smile and started the car.

She gave herself a stern reminder that the handsome Brigadier was a trained killer, and her new boss; then tried very hard to think about meteorites.