Title: The Monster in the Dark

Author: Nemo the Everbeing

Summary: Some things must be dealt with, and Ace put off dealing with the cheetah virus until it was almost too late. The Doctor must enlist some unconventional and unwanted help to pull her through.

Spoilers: General series warning, as well as specifics for "Survival."

Disclaimer: This is not mine. Well, okay, the story concept might be, but even that's iffy, since I'm just riffing on themes the series was already addressing. Doctor Who, the Seventh Doctor, Ace, and everyone else from the Whoniverse who happens to make an appearance in this story belongs to the BBC.

Authors Note: Without the following people, places and things, this story would not have been possible. In no particular order, I'd like to thank: Sylvester McCoy and Sophie Aldred, the Dustbowl, Roger Delgado, bumper-nose crabs, Anthony Ainley, Scum Beach, Greek mythology, Joss Whedon, and the entire country of Jordan. Oh, and an extra-special shout-out to my phenomenal beta, Zircon. Thanks!

oOo oOo Prologue: A Shadow in the Halls oOo oOo

In her dreams, Ace chased a great cat through the halls of the TARDIS. It glided through the dim corridors, its loping paws making no sound as they connected with the floor. She saw it in the distance and around corners: golden eyes flashing from a tawny face.

Weren't TARDISes supposed to guard against giant cats?

She followed the cat. If she could catch it, she thought she'd be able to figure out why it was there in the first place. She followed the cat, although her plan on what happened after capture wasn't as clear as she would have liked. You couldn't really interrogate a cat. A cat was the kind of creature which would never give up its secrets. Sort of like the Doctor in that respect, was the cat.

In every dream, she would nearly catch the cat. She would turn a corner and there it would be, sitting on its haunches waiting for her. She would backpedal and it would stare, and she'd know that it had already won.

And then she would wake up with the pain of elongated teeth and the shock of heightened senses. At those moments, in the dark of her room, she felt infinitely connected to the present and the world around her. She could see every imperfection in the smooth ceiling and hear the heartbeat of the TARDIS coming from so very far away. She could taste the tang of invented air. She could feel the tingle of minute adjustments in the spatial parameters of the ship shiver across her skin. And she could smell the Doctor. No matter how far away he was, or what he was doing, she could smell him: old books, ozone, confectionary, and the barest sigh of an alien breeze carrying spice and honey-sweet flowers.

She would rise, clad only in her T-shirt and underwear, and she would pad out of the room. Every footfall was deliberate: first her toes silenced the impact, and then the heel settled with fluid deliberation. Her feet wove delicately, one in front of the other. A perfect line of attack.

She would wander the halls, not sure who she was pursuing or if she was pursuing anyone at all. Perhaps she was hunting shadows, but the drive within her told her to chase, and so she did.

She caught glimpses of the great cat out of the corners of her eyes, flashing through the gloom of parallel corridors. It happened every time, each the same. She knew she wasn't dreaming—she felt a dizzy rush of disbelief that this thing existed in the real world as well as her head—but she couldn't let surprise or doubt deter her. She would spring into action, and her feet would slap the deck like thunderclaps as she flew after it. Her teeth would flash and her eyes would grow even more feral and she would hunt in earnest, running down the beast which dared violate her territory and threaten her Doctor.

She knew something was wrong with her. She had no doubt it was the cheetah virus. The Doctor had said she would deal with it for the rest of her life. She just hadn't imagined that dealing with it would be such an immediate affair. The logical thing, of course, would be to tell the Doctor that they were experiencing some sort of giant cat infestation. It was the kind of thing the Doctor would want to look into. She never told, though. Dream after dream, night after night, and she never breathed a word. She couldn't. The great cat was for her alone, and the Doctor wouldn't understand. He wouldn't be able to help, and he might even be hurt. Better to hunt the cat on her own. Track it down and pin it in a corner. Fight it. She wondered what the statistics were on a nineteen-year-old girl versus a giant cat.

She would chase throughout the night, and the next morning she would awaken in some strange room dressed only in her T-shirt and underpants. She would pull herself to her feet, tug the hem of her T-shirt down, and sneak back to her room, ghosts of the previous night flitting in her wake.

She told herself that it was nothing she couldn't handle. Ace McShane wasn't scared of anything, let alone some great imaginary cat in the dark. It was just her fears and worries finding form. It was her mind trying to cope with the disease by giving it solidity. She would get this out of her system. She would calm down. Things would go back to normal. She would just be Ace, and she wouldn't wake up in the middle of the night as something else. Something with the inescapable need to hunt and kill the great cat. The cat, which, in the end, would always be sitting around the bend waiting for her. The cat which stared at her and knew her. Knew every inch of her.

She wondered if the great cat was her.

After months of this hell, she sat in the kitchen with a cup of coffee at her elbow. She was being worn thin by all this nocturnal dashing about and it was showing in her caffine intake. She was surprised the Doctor hadn't noticed, but then, they'd been busy. He was finally getting around to doing some repairs he'd been meaning to catch up on for the past two centuries. He'd torn apart several walls, had pried off multiple face-covers from the main console, and he would frequently vanish so far into the bowels and underpinnings of the TARDIS that even Ace didn't know where to start looking.

She'd tried to get him to teach her what he was doing so she could help with the upkeep. She thought it might be nice to be able to look after the ship for him so that he didn't have to do all the repairs in one it's-necessary-or-we-could-implode/explode/deplode-or-any-other-kind-of-'plode-you-might-happen-to-think-of blitz. He'd also seemed rather keen on the idea.

So she'd sat down next to him at the console. She'd handed him tools and listened to him lecture on the finer points of TARDIS repair, but her mind had begun to wander. She'd seen glowing amber eyes through the door to the rest of the ship, and she'd stared back at them for minutes at a time, leaving important gaps in her education. She'd been too ashamed to ask the Doctor to repeat himself.

After a while she began to beg off the sessions, and she thought she'd seen a flash of disappointment in his eyes. She'd said she had to digest what she'd already picked up and he'd accepted the answer, so it wasn't as though he thought she wasn't interested. Maybe he just liked the company.

Now, instead of working with the Doctor, she sat alone in the kitchen with a cup of coffee and a desperate desire to just have it over. She wanted the virus gone. She wanted to be able to sleep through a night or learn something useful without her own subconscious having to step in and do a little tap-dance. If she'd had the energy, she might have smirked at the image in her mind of the great cat wearing tap-shoes, springing up from its seated elegance to do its very best Fred Astaire impression. She was too tired though, so she sipped at the coffee and willed herself back to life.

Perhaps a plate of waffles was in order. She'd been off her feed for a few days and she needed to get back to it. Proper nutrition was just the thing for sick bodies. Ace dragged herself to her feet and shuffled to the food dispenser. She stared at the controls in bleary incomprehension for several seconds, then shook herself out of her reverie and punched up a plate of waffles, extra syrup.

A bright yellow cube came flying out of the dispenser and smacked her between the eyes.

Before she could properly formulate a response to the utter randomness of the occurrence, another cube hit her. Then another. The next thing she knew, she was being pelted with a shower of yellow cubes. She batted at them to no avail.

"Doctor!" she bellowed. It had to be his fault. He was the one mucking about in the TARDIS' innards day-in-day-out, and she had no great belief in his ability to command the machine. He'd probably crossed some wires or he'd torn the food machine apart and never bothered to put it back together. Leave it to Ace to clean up the mess.

She waded through the cubes—which were now almost a foot deep about her feet—held one hand out before her and aimed for the emergency shutdown button. Everything on the TARDIS, she thought, should have an emergency shutdown button. One thing she'd learned from three years in the dimensionally transcendental police box was that anything on the ship could and would do something insane like spit yellow cubes when she least expected it. Especially with the Doctor's current maintenance schedule of 'I'll fix it when it's broken.'

She snarled, lunged forward and slapped the button hard enough that she cracked its smooth face. The long, thin fissure in the material caught on her hand and tore her palm. The scent of blood hit the air and she stood, panting, as the deluge ceased. Each inhale dragged a growl from her.

The realization that she'd changed—that she'd turned into what she was beginning to refer to as her 'crazy, yellow-eyed catgirl' persona and she hadn't even realized—didn't horrify her. She was still too angry and too on edge to respond as she should. She smelled the blood in the air and felt each cube brush against her legs. The growls rumbling her chest felt like she was finally releasing a tension which had built for weeks. She was powerful. She was in control. She faced a situation and she solved it. Her life was boiled down to its simplest possible form and she found she liked it that way.

After several moments of standing and reveling in her state she began to calm, and the worry began to seep in around the edges of her euphoria. She wasn't changing back. Her teeth remained sharp, and her senses were still hyper-acute. She stared at the cracked button on the food dispenser and the nausea of fear swept through her. If she couldn't control herself over something as trivial as a malfunctioning food machine, she was in trouble. She could do horrible damage and she'd never notice. No, scratch that, she'd notice. She just wouldn't care.

And what if the next time it wasn't a button in her way? What if it was—

"Oh, dear!" the object of her fears said from the door.

Ace had her back turned to keep her face hidden, but she knew it was the Doctor. She would have known even if he was unmoving and didn't speak. She could smell him, hear his double-heartbeat rushing in her ears. She drew a ragged breath. She'd never been so close to a real person in such a small space in this state, and his presence was almost overwhelming. His scent had nowhere to go, so it filled the room. It was packed so tightly it blocked out all other scents.

He bustled over to the food machine, not commenting on her lack of response, and pulled the facing off to reveal an intricate tangle of wires and feeds. He followed two at once with his fingers. Ace peeked over her shoulder to watch.

He asked, "Tell me what happened. Was this in response to a particular command, or just out of the blue?" She still said nothing, because as soon as she spoke he would know. Her voice got obscured by the fangs.

He was expecting a response, though, and when he didn't get one he turned. Ace made to whirl away, to look busy cleaning up the cubes or something, but she had been caught unawares. Even her heightened instincts didn't allow her to turn quite fast enough.

The Doctor straightened, and his attention was completely diverted from the malfunctioning food dispenser. "Ace?" he asked, his eyes never leaving hers. She could see every fleck of blue and gray in his irises, could define every hair on his head.

She swallowed hard and glanced away, reeling from sensory overload and the palpable presence he created in the room. "Just . . . just give me a second," she whispered.

"Has this happened before?" he asked. Damn him! Didn't he understand what 'give me a second' meant?

"No," she snarled, and they both knew it was a lie.

She didn't need his help, though! Anything he did at that moment was just going to make things worse, because to do anything he would have to come closer, and when he did that—and there he went, stepping towards her like the idiot he was. All she could smell was his blood, and all she could hear were his pulses, and who really needed waffles when there was something so deliciously trusting just standing there?

She had him by the lapels and slammed up against the food machine before he could react. He let out a startled whoosh of breath, and his hands came up, but he didn't try to push her away. Why was he not fighting? Even the weakest prey fought to keep their own lives. Why did he offer himself up to death?

She leaned in, willing her prey to understand, to fight. Such unresisting sacrifice made the kill unappealing. She grazed her teeth over the jugular, and he whispered, "Ace?"

Ace? What was he talking about?

"I could tear your throat out right now," she said, wanting the struggle more than she wanted the kill. She had been spoiling for a fight all four months since the cheetah planet. "Do you know that?"

"Yes," he said, and she could feel the vibrations of the word under her teeth. There it was. That was fear she heard. She purred low in her throat, all approval. If he was finally going to cooperate, she was more than willing draw things out a while, bat him about a bit.

"I could snap you like a dry twig," she whispered. He shuddered and she ran her tongue along the vein, collecting her very first real taste of her prey. Such ancient blood, she thought. Did he have any clue how attractive that was? "Would you fight?" she asked, knowing the answer, but wanting to hear it from him. She wanted that fear again.

"No."

"You should." She adjusted her grip, smoothing her hands from his lapels to his shoulders and then shoving hard. There was a dull thump as he was forced ramrod straight against the wall.

"Ace," he said again.

What was he on about, anyhow? Who was this—

Ace.

She was Ace.

She jerked away, gasping as the veil of predatory intent fell and everything came back into focus. She had almost hurt the Doctor. She had almost killed the Doctor. She'd shoved the Doctor against a wall, threatened him, and . . . Gordon Bennet, what she'd done to him.

He stepped forward, but she was already running. He called after her, "Ace!" but she was out into the hallway and sprinting away. She had to get somewhere, had to find a solution. It was one thing to lose sleep and have nightmares about great cats, but she wouldn't allow herself to hurt him.

She staggered to a stop in the med-bay. She wondered if the TARDIS had led her there with intent, or if it was just a happy accident. The end result was the same either way: she knew what she had to do. If the cheetah came out when she was angry or afraid, then she had to ensure that she wouldn't feel either, and if the physical changes were basically to do with musculature and maybe a bit of brain chemistry, well, there was a fix for that too.

Let it never be said that Ace McShane didn't know how to plan. After all, she'd sat at the feet of the king of master plans and she'd learned well. It was all about calculated risks. About weighing potential harm against potential benefit. She did that in seconds, and her conclusions were simple. They'd have frightened her at any other time, but she'd almost killed the Doctor. All fear for herself had departed the second she'd done that.

She tore into the neatly-organized cupboards. It wasn't long until she found the two doses she was looking for. She plugged the first into the delivery-gun and pressed it to her throat. Then, taking a deep breath, she pulled the trigger.

She felt the muscle-relaxants begin to kick in almost immediately. She slumped against the exam table. She kept her feet under her, but it was a struggle. She had seconds to administer the next dose before she was rendered incapable of doing so. With limp fingers barely able to grip let alone maneuver, she loaded the second dose into the delivery-gun. She shot the dose home even as her arms felt dragged down by lead weights.

The massive dose of sedatives entered her system. The world slewed. She wondered if, perhaps, the doses weren't measured out to human physiology. That might be a problem. Then again, they were doing what she needed them to do. She wasn't a threat to anyone in this condition. Now, if only she could get the med-bay to stop tilting sideways . . .

Her knees buckled and Ace fell to the floor, lying there as her eyes fixed on the great cat standing in the doorway. It would come after her only when she was weak.

"Come on, kitty," she said, but the words came out thick and slurred. "Come and get it."

The cat leapt, growling, and slammed into her.