With the sonic screwdriver out of action, the Doctor was temporarily stumped when they came face-to-face with a sturdy, imposing wooden door. This street was narrow and old and, by the look of the squat buildings, extremely poor. There was no one around despite the rapid approach of morning, for which the Doctor was thankful when Jack charged past him and introduced his shoulder to the woodwork with extreme force. The door held and Jack bounced harmlessly off, grunting in pain and frustration.

"Completely solid," he reported.

"This is only the front door," the Doctor reminded him.

They skirted round the side of the building, down an alleyway so narrow that Jack had to walk sideways. There were no other doors or windows on this side, but the wall of the building soon gave way to a high iron fence topped with barbed wire. Jack stared up at it, then shook his head.

"We'll rip ourselves to shreds climbing that."

"Yeah," said the Doctor, ambling along the length of the fence. "So good job there's a gate. Long way from the street though. Odd that. Never mind!"

The gate was padlocked, but the Doctor pulled from his pocket something which looked suspiciously like a hair grip. Jack raised an eyebrow.

"It's amazing what you pick up when you travel the universe with an assortment of young women," said the Doctor cheerfully, as the gate sprung open. He put up a hand to hold it shut, then seemed to listen intently.

"I can't hear anything," murmured Jack.

"That's 'cos apes weren't designed for hearing. Not much to listen for way up in the trees, but on the inside of a suspiciously well-defended newspaper office, you'd be amazed what you can deduce with hearing like mine."

"Like what?"

The Doctor pulled a face. "We're not alone. Some kind of creatures…" They exchanged a glance which said quite plainly, we're not going to find out what it is hanging around out here, and the Doctor pushed open the gate.

Inside was a large area which had probably started out life as a domestic garden. The Doctor pressed his back to the fence and edged to the right, towards the building. Jack carefully closed the gate and squinted into the gloom.

The first impression he got was of bars. Dozens of cages were arranged around the courtyard, some large like aviaries, some smaller, like rat cages, and from them came a variety of subtle sounds. Invisible things rustled in the darkness, and Jack felt a shudder run up his spine at the memories of his two encounters with the shadow thing. Occasionally something squeaked or grunted. As he strained his ears, Jack could make out a larger sound, lower and deeper, like a huge animal stirring in its sleep, but he couldn't pin point where it came from.

"Private collection?" he mused.

"Dunno." The Doctor ambled across to the nearest cage and squatted down beside it. Jack's hand moved unconsciously to his hip, where his gun was safely holstered, then he chided himself. Whatever was in there couldn't be any bigger than a rabbit.

The Doctor, however, wasn't taking any chances. He gave the sonic screwdriver an angry shake, which failed to help in any way, then resorted to feeding a leaf into the cage to see what happened. Childhood memories rose in Jack's mind, and he expected the leaf to be yanked away and gradually eaten down by some furry, loveable critter.

Instead the cage lurched and the Doctor fell back on his bum, startled. "That," he said, "is no bunny rabbit."

"Alien?" Jack asked.

"Don't think so. Not alien. But there's much worse than alien, if you think about it."

Jack had to admire the Doctor's courage as he reached for the box again.

"Who's a pretty boy then?" the Doctor coo-ed, carefully sliding back the little wooden door in the side. "Who's a fluffy-wuffy freak of nature, eh?"

Something shot out of the cage, and the Doctor lunged at it. It wriggled out from under him, and Jack got the impression of dappled fur and long legs before it vanished into the night.

"Oops," said the Doctor.

Jack stared around at the cages. A few of the creatures stirred in response to the commotion, but nothing really seemed interested in breaking out and attacking them. "Exotic pets?" he wondered aloud.

The Doctor picked himself up and brushed dust and straw off his trousers. "Very exotic. About as exotic as they come. Someone's been playing with a make-your-own-mutant kit. Someone who's not much actual cop with this sort of thing."

"So the newspaper office-"

"Is a front for something way more interesting."

The Doctor grinned in the dark. "You up for some investigating, Jack m'boy?"

He didn't wait for an answer as he scurried off towards the house. Jack trotted after him, padding on silent feet. He didn't know what to expect from this strange place next, and decided he should be prepared for absolutely anything; he still jumped in surprise when the back door slammed open and three people ran out into the garden. Jack cursed his unease – he was never this nervous, whether he was facing blood-thirsty monsters, or just other men with better weapons than he had. He knew the shadow creatures had somehow gotten inside his head and triggered his primal fears, but damn them, did they have to take his style away too?

"Brilliant," said the Doctor cheerfully. "Just the blokes I wanted to see. The blokes and the lady," he corrected himself, winking at the female member of the group. "I was wondering if you could help me with something, you see I-"

"Shut up," said the apparent leader, a tall young man with cropped blond hair. "You're trespassing."

The Doctor's eyes widened in surprise. "Are we? Crikey, I'm sorry. Here, Jack, did you realise we were trespassing? I had literally no idea-"

"Shut up," said the blond again. "Who are you? Show some I.D."

Within moments The Doctor was shoving his psychic paper right up to the man's nose. "There you are. I.D. Happy now?"

The man's eyes widened. "Sir! I'm sorry. Let us escort you to the labs."

"Too right."

The three newcomers led the way into the house, their demeanour now far less aggressive. The woman and the dark-toned man kept glancing back at the Doctor, their expressions a mixture of awe and curiosity.

Jack raised a questioning eyebrow; the Doctor shrugged and shook his head. It would clearly be interesting to find out who these people thought he was.

They were escorted into the house through the back door, which faced onto a flight of stairs. Blondy led the way up, into a long, narrow passageway with several doors off it. The Doctor and Jack were ushered through the first door, behind which was a small, dimly lit laboratory. Heavy blankets covered the windows, and the only illumination came from two thin strips on the ceiling. Like every good lab in the universe, this one was lined with shelves of mysterious things in jars. Weird, eyeless faces grinned out of the gloom, until Jack realised they were skulls – some human, some animal, and some quite definitely alien.

The middle of the room was dominated by a large work station covered in technical equipment, data pads, and bits of paper. The Doctor made straight for it, grabbing a weird, convoluted tube and breaking into a delighted grin.

"An amino acid extractor! Haven't seen one of those in years. That's a nice bit of kit. Means you're breaking down and re-arranging DNA. Genius! Oh," he added, his expression clouding over, "but that's bad. That's really, really bad. I mean really, really, really, really-"

"Put that down."

The Doctor blinked in bemusement, as if the words made no sense to him. Jack was impressed – the voice wasn't loud or particularly stern, but it contained an air of command which made Jack want to snap to attention. A man detached himself from the shadows of the far side of the room, and held out a hand for the extractor.

"Don't think so," said the Doctor, and he casually smashed the tube on the side of the workbench.

The man's expression did not change. In his early fifties, and dressed in a plain suit and bone-white lab-coat, he met the Doctor gaze for gaze.

"Do you realise how much that piece of equipment cost?"

The Doctor shrugged. "Ten a penny where I'm from."

"And where might that be?

"Oh, just a little planet you've probably never heard of. I'm the Doctor, by the way, and this is Jack Harkness. Say hello, Jack."

"We found them near the cages," said Blondy. "They let one of the creatures loose."

"Which one?"

"Looked a bit like a vorchut," said the Doctor helpfully. "Kind of giant rabbit thing with spindly legs… nasty little buggers. I didn't catch your name," he added, holding out a hand to the grey haired man.

"Say the word and we'll get rid of them," said Blondy.

"You'll try," Jack growled, hand on his blaster.

The Doctor made a dismissive noise. "Scientists killing people? Biggest bloody waste of flesh in the universe, scientists that kill people. You want to be discovering things and pushing back frontiers and… well, mucking about with stuff you shouldn't, but you seem to have a good grip on that one. But killing people? That's the sort of thing science is supposed to stop. You're meant to advance humanity, not haul it off and have it quietly extinguished in a little room with a great big padlock and soundproof walls."

The older man coughed discreetly. "He meant throw you out. Killing you would indeed be safer, but we do not stoop to savagery here."

"Oh. Sorry."

"Quite." He held up a device which looked like a small digital camera and pointed it at Jack.

"None of that, thanks," said the Doctor, snatching the thing out of his hand. "We've both had our share of memory misadventures, ta muchly. We'll be keeping all we've seen up here though, don't you worry." He tapped his forehead to emphasise his point.

"Yeah right," said Blondy. "You're obviously spies."

"We're obviously no such thing. If I was a spy, I'd have come in the dead of night and shinned up the drainpipe, not at the crack of dawn and through the gate."

The impassive face of the chief scientist moved for the first time; he raised an eyebrow.

"I believe you," he said. "But if you are not spies, then who are you?"

"You… believe us? Just like that?"

"Yes."

"We're travellers," said Jack. "Just explorers."

"And it seems to us you've got a bit of a problem re some all-consuming new religious bods who popped up over night. Thought we might, you know, lend a hand, see what can be done, but if you'd rather we leave…"

He seemed to mull it over, then extended a hand. "My name is Dr Comma. And you are correct. We do seem to have something of a problem."

The Doctor pulled up a stool and sat down. "Tell me."

"Very well. Although I find it hard to believe you are on this planet, yet know nothing of the Light."

"Like we said, we travel. A lot."

Dr Comma waved a hand to dismiss his lackeys. Reluctantly, Blondy left the room, followed by his accomplices.

"It started six tears ago," said Comma, in that clipped, precise voice. "In London. Representatives of the major religions – Christianity, Islam, Hinduism, and the like – were meeting with the Prime Minister and his cabinet to plead their case. They longed to cling to the last vestiges of their waning power, but the Prime Minister was reluctant. He wanted any religion with a significant influence on people's thoughts to be disbanded, and with good cause. He had much support in the scientific community, and in the general population. After the last war, who can claim the churches were in no way responsible for countless deaths? No, organised religion is dangerous. And the Prime Minister was right to try to abolish it."

"What happened?"

"The meeting went badly for the representatives. I was there, as a scientific advisor to the government. The cases presented were weak and badly prepared, and I was able to dismantle any credibility they still had. Half way through the meeting, something happened, something which, to this day, I cannot explain. A being appeared in the room, luminous and radiant. Humanoid. Hovering just above the floor, arms wide as though to embrace us all. It struck down the Prime Minister and killed him instantly. Then it told the group of representatives that they were all right – and that they were all wrong. They were to unify, to join forces, to become one. And they all believed what they were seeing was the physical manifestation of the deity or deities they had devoted their lives to."

"…And?"

"They did as it said. Christianity was abolished, and Islam forgotten, and Judaism torn down like the Tower of Babel. Even the token Buddhist of the group believed he was seeing a Buddha, but… well, we all know what happened to those philosophers. The various establishments joined together to form the United Divine Order. Religious fervour gripped the country, and then the continent, with everyone worshipping this entity that called itself The Light. It took little time for the new religion to spread across the seas, but this deity was eager to present itself to humanity, so its existence is undeniable. All people converted. In America, in Africa, even in Asia. Rebels are struck down. Anyone voicing doubts is hunted and put on trial, if they're lucky. But that is not all.

"A fleet of ships were approaching Earth. Nobody knew about them. It took time until our sensors detected them, and panic started to spread. Five years ago, shortly after the last of the American Bible-Belt was converted, the ships entered Earth's atmosphere. Hundreds of them! The size of cities, and bristling with weapons. Torchwood was disbanded by the Unity, so we were defenceless. Or so we thought. The Light rose from the ground and shot towards the fleet. There was a moment of extreme brilliance, and the fleet was gone. There was no aftershock, no radiation, no sonic boom. They were just… gone."

Jack frowned. "You're saying you believe in this… Light thingy?"

Dr Comma shrugged. "I have seen it with my own eyes."

"But you hide up here. In the dark."

"I do no submit, if that's what you mean. I do not worship any entity, and I do not acknowledge its divinity."

"Good!" said the Doctor. "We might just have a chance of fighting it, then."

Comma laughed. "Fight it? Be reasonable, man! We don't even know what it is."

"No, but we're going to find out. Me and Jack, we'll go out there and find it. Then we'll figure out what to do."

"I'm sorry, Doctor." Comma shook his head. "I believe you are indeed on our side, such as it is, but you must remain here for the time being. The risk that the Unity may find us is too great. We use… certain subtle methods to draw those who would join us here, but they are put through many tests to determine their loyalty. We can take no risks."

"But this part of town is safe, isn't it? Not controlled by the Unity?"

"It is… ignored, for the most part. Every so often they try to move in and destroy what vestiges remain of the old religions, but we do them little harm, and they have more pressing concerns. Nevertheless, this area is small, and you may find yourself lost and captured. You will remain here."

Jack began to protest, but the Doctor shook smiled. "Fine. Good. There's lots I want to see here. Lots of questions to be asked. Like why the heck you're breeding mutant rabbits in the back garden. And where you got all these skulls. And why this Light thingy didn't kill you when it struck down the Prime Minister…"

Comma opened his palms in a gesture which said the answer should be obvious. "I am a man of science, and I saw The Light with my own eyes. It let me live so I could sway the opinions of my colleagues. When I expressed my doubts, the Unity proclaimed me a wanted man. If they find me, they will kill me. I have caused them too much trouble – but not enough that they are actively searching. For now."

"This thing's gotta be an alien," said Jack.

"The Light does not allow aliens on Earth."

"Because it is one, maybe. Doesn't want it's story rumbled. Some other advanced species could give the game away, tell everyone it isn't actually god."

The Doctor nodded. "I'm thinking much the same thing. If I can find out where it's from, and what it's up to, I reckon I can put a stop to it."

To be continued…