The Doctor had talked his way into the rather Fort Knox-like compound with the help of his psychic paper. Rose, who had developed a thing about high-tech gadgetry since meeting him, was slightly disappointed at the sight of the solitary, plain concrete building, and felt it was a bit of an anti-climax.

But on entry she soon cheered up.

The floor and walls were made of a black, stony substance not unlike marble, which reflected the light so that the whole area seemed to radiate a strange glow.

At the back of the large entrance room, there was a bubble of black glass, through which a Myvian could be seen surveying a huge bank of security screens. More black panels of glass slid back and forth to admit more people to and from the already bustling reception area.

Rose grinned. "This is like a 5-star hotel!"

Jack whistled in appreciation, but she couldn't tell if it was because of the sophisticated décor, or a rather striking male Myvian who had just walked by.

"Yeah, it's all a bit swish, innit? Very Star Wars an' all that. " the Doctor said. "Mind you, it's not so glam if you're a prisoner."

"And that's said from experience, I suppose, knowing the trouble you get yourself into," said Rose.

"Or maybe just because I know everything," he replied teasingly. "But I got banged up in here within half an hour of my first visit. Bella was sent to interrogate me. Not that she got very far, since I hadn't actually done anything wrong, I only… "

"Talk of the devil," said Jack suddenly, as Bella appeared at one of the doorways, and came sprinting towards them. She looked uncharacteristically flustered.

"There you are," she said with obvious relief.

"Where's your little shape-shifting problem then?" the Doctor said brightly.

"That's the problem," Bella said. "We don't know."

She directed them through the door she'd just emerged from. She pressed her hand against a white circle on the glass, which glowed, and with an affirmative beep the door slid back.

"Fingerprint recognition, or DNA?" Jack wanted to know.

"Fingerprints. And that's another part of the problem," Bella explained, as she led them down various passageways.

"The shape-shifter escaped nearly two hours ago. It can change at will into the appearance of anyone it sees. A couple of years ago, we had swipe cards, in which case the creature would have been trapped, because it can't replicate solid objects. But because of the semi-telepathic link it forms with its subjects brain, the likeness even extends to fingerprints, potentially enabling it to have access to every room in the building."

As they descended a second flight of stairs, Rose was beginning to realise how big the HQ was; it continued deep underground.

"At the moment, we've got it contained in Sector 24. At least, we hope we have. There haven't been any reports of unusual behaviour in any other sectors."

"What sort of behaviour?" Rose enquired.

"Aggression, mainly. But otherwise it's almost impossible to tell the difference. As well as imitating the voice, some people are saying it can impersonate personality as well…"

"So what type of shape-shifter are we talking then?" the Doctor asked.

"A Healdon. That's where I thought you could help, Doctor. Do you know them?"

"I've come across them before," he said, then frowned. "But what's a species like that doing here?"

Bella waved her hands around in a display of agitation. "I don't know," she said.

The Doctor's serious expression deepened as they reached the entrance to Sector 24. Beneath the sign, it read simply: "Laboratories".

"Now this is too much of a coincidence," Rose heard him murmur.

There were extra precautions being taken at the only entrance to this sector. Two Myvian officers, dressed in shining black, and both armed, were guarding the double doors. After a few minutes of intensive questioning on both sides, they were admitted.

"Well I suppose the best place to start would be the original holding area –" Bella started, then the clatter of footsteps on the stone floor halted her.

A male Myvian came sweeping around the corner towards them. He was tall and imposing, wearing a floor length coat (not surprisingly, black) with a high collar that reached the tips of his ears. His skin was such a deep purple that it appeared nearly black; but it was his fiery red eyes which completed his intimidating appearance. To Rose he looked like the devil incarnate.

"Officer!" barked the bat out of hell.

"Commander…" Bella scooted up to him, raising interlocked hands in a kind of salute.

The Myvian pulled her aside and began speaking to her in a low, abrupt tone, which made it sound like she was being reprimanded. All the while the menacing eyes regarded the newcomers with a mixture of interest, suspicion and hostility. The Doctor met his gaze, and Rose felt a glimmer of triumph when the Myvian lowered his eyes after a few seconds.

With a final audible "I want this sorted.", the commander strode briskly out of sight into the silent depths of Sector 24.

"Problems?" the Doctor asked lightly. Bella swore under her breath, once more looking rebellious.

"He's just worried about his reputation if this gets out." She sighed, then took a deep breath, composing herself and returning with speed to her usual tough exterior. "Is there a way of preventing the Healdon's metamorphism?"

The Doctor thought for a second. "It's possible that by decreasing the indicension factor of time and suspending the causitive…. Basically, yes, I think so," he replied to the puzzled faces around him. "With the Tardis, yes. But how we'd capture a shape-shifter is a whole different problem."

Jack glanced around the deserted corridors. "Hey, Doc, you could fly the Tardis in here, right?"

"This whole compound is surrounded by a force field," Bella interjected.

"I shouldn't worry, the Tardis is capable of – " The rest of the Doctor's words were drowned out by a sudden shattering of glass. Close. Jack whipped out his blaster, and Bella was suddenly clutching a complicated, nasty-looking pistol, using three hands to manipulate its various controls in preparation for firing.

The sound of footsteps crunching broken glass penetrated the sudden silence. Heading away. The Doctor sprang into action, sprinting cat-like down the west corridor, to where it turned 90 degrees into another. Flattening himself against the wall, he inched forwards and peered round.

The window panel adjacent to "Lab 14ΞǾ9" had been cracked. That surprised him; it was similar to bulletproof glass and would take great force to damage. But the source of the glass was the overhead lights, resulting in near darkness where the bulbs nearest to him gave out. He couldn't see anyone, but his senses told him that someone – or something – was close.

Then, through the window, he caught movement in the darkened room beyond. Then sound – a muffled cry.

The Doctor wasn't happy with this situation. Of course he wasn't in the least bit frightened; if anything, he was worried for the creature. As much as he liked Bella, he wasn't generally fond of the rest of her race. They were the most powerful species in this galaxy, and knew it. They reminded him of things he'd rather not think about.

And now, a supposedly "lesser" sentient being was in their laboratories, being hunted down. And he intended to stop it. He strode over to the door, and without hesitation, pushed it open. Behind him, Bella gasped.

…OK, finally something closer to action…. Please tell me what you think everybody ! Chapter 5 coming up. (Blame my mum for putting the whole bat out of hell thing into my head)