A/N: Hello, and thank you for at least looking in this story. By the way this is my first Star Trek and Doctor Who fic here, so please tell me if I got anything wrong, constructive criticism is completely welcome! Anyway, I hope you enjoy!

Skin Deep

Part 1: Windows to the Soul

Deep in the maintenance ducts of the enterprise, shrouded in shadow and surrounded by silence, it waited. Starving after so many years alone in the black void of space, it could hardly restrain itself with the overpowering scent of prey so close. The dim senses swung towards the sound of approaching footsteps. Yes, come closer, come to your doom it whispered to whatever dim witted creature was approaching its hiding place. First it would have this one as a host, then it would feast on the life-force of all those in this pathetic vessel.

The prey came into attack range and It unleashed its attack. A flash of crimson material registered on its senses, but that was unimportant, all that mattered was the prey. It was all over in a matter of seconds, and the Skin-Walker claimed its new host.

No one had noticed when Ensign Kenway entered the maintenance ducts, after all, he was a security officer on patrol, and it wasn't anything out of the ordinary. No one noticed when it wasn't Ensign Kenway that exited the shadowed tunnel, and yet another red shirt crew member was lost.

The TARDIS was usually a rather patient being, and she was fond of the Time Lord who traveled with her. Most of the time at least. There were days (like this one for example) that he really got on every last nerve. Though he was in his tenth regeneration and more than old enough to know better, the silly man insisted on doing things like hitting her console with a hammer. Usually this was an excusable offence, it was nothing more than a flick really, but at the moment, the TARDIS was well out of the mood to put up with it.

She was very aware that her doctor wished to go to the now found moon of Poosh. Yes, she also knew he wanted to go now, but if he hit her console with that hammer one more time… As the Time Lord raised the hammer again, the TARDIS lurched to an abrupt stop and refused to move an inch (or a second) more.

The Doctor smiled, apparently satisfied with this and pocketed his Sonic screwdriver on his way to the door. Without looking outside, he strolled out and shut the door behind him. The TARDIS smugly locked it behind him and set about rearranging several of the back rooms. It took only a few seconds for the Doctor to realize that he was not in fact, on the previously lost Moon of Poosh, and he tried to re-enter the console room.

The TARDIS debated with herself momentarily, should she let him in? He surely got the message now… But he did almost die only a few days ago, technically he did. So for now her doors remained firmly closed, he would learn to be more aware of his surroundings or he would get locked out somewhere he didn't want to be. Now decided, the TARDIS returned to rearranging rooms, completely ignoring the Time Lord attempting to push in her doors. Maybe if he pulled, like the sign said she would let him in…

_
The Doctor eventually gave up on entering the TARDIS, he got the feeling she was mad at him for something and didn't want to risk making her more so. She might pull something worse than dropping him somewhere he didn't want to be if he did. Like that time when he tried to open the door and she had parked too close to the shipping crate and he couldn't get out. It had taken multiple apologies and a promise of a wash to get her to move.

This train of thought was appropriately derailed as something else occurred to the Time Lord. Where exactly was he? That would probably be a good thing to know… The Doctor looked around, nothing visually gave away his location, just empty hallways with an obscene amount of light fixtures. Nothing that really stood out and could offer any sort of clue as to his location.

The Time Lord crouched in the middle of the hallway and ran his index finger along the smooth metal plating. In an action that would have every mother of a toddler smacking his hands, the 900 year old then stuck the digit in his mouth. He pondered for a moment, seeming to roll the flavor around on his tongue, then smiled brightly enough to rival the lights around him. "The Enterprise! Lovely ship that one!" and he continued on his merry way, content with the impromptu visit to the Federation ship. He could spend a few days here, just watching the crew do what they did, always a pleasure to visit a well maintained vessel…

As he passed a maintenance shaft, the cheery bounce of his footsteps slowed and then stopped altogether. He was getting that feeling again. The one he always got when there was a mystery afoot, one that he would naturally have to help solve. Peering into the shadows, the feeling was once again confirmed. Hidden in the shadows of the empty duct, lay a man in a red uniform, his face twisted and frozen in horror, dead. His pupils were missing, leaving only the whites of his eyes to stare sightlessly at whatever had killed him. The Doctor carefully bent to one knee before the fallen man, fitting dark rimmed glasses over his eyes, his own face twisted with sympathetic concern as he ran his sonic screwdriver up and down the length of the body.

In a motion he definitely hadn't practiced in the mirror (which most certainly didn't result in him accidentally throwing his sonic and almost losing it) the Time Lord flicked his wrist and studied the tiny screen of his screwdriver. It was not an encouraging exercise. "Oh," he said, standing and physically distancing himself from the body as if it were diseased "Oh no…"

Part 2: Spock and the illogical, terrible, no good rotten day.

Thefirst body had been worrying. The second highly suspicious. Now with the count up to three, the crew of the Enterprise was officially on alert. Kirk, who is Spock's opinion was illogical on the best of days was nearly insufferable, not that the rest of the crew was any better, all of them peeking around corners and into shadows, constantly on alert for whatever was picking them off. If it wasn't such a serious situation, Spock would have compared it to the time of year when McCoy prowled around the Enterprise, searching for whoever was next on his list for a physical (Who would be next?). Then the crew displayed almost the same paranoia, constantly checking doors for the doctor, making sure he wasn't near. Except McCoy hadn't killed anyone (that they could prove) and whatever this was, had already killed three. The Vulcan himself managed to be on alert without timidly peeking around corners and jumping at shadows so he thought it rather illogical for everyone else to continue the practice, even if it was understandable.

Spock was forced to abandon his ponderings as he and Kirk arrived in the infirmary, hoping that McCoy had found something new on the most recent body. The doctor looked up as they entered and sighed, covering the horrified face of a female crewmember. Kirk looked halfheartedly hopeful as he asked "Anything?" but just as before, the medic only shook his head.

Meanwhile, the Doctor kept to the shadows, he had no desire to attract the attention of the senior crew members. Internally he cursed their timing and his, the Time Lord had really been hoping to get a quick look at the body himself, or at least a look at what McCoy had, but then the man had come in himself, followed closely by the captain and his first officer. Kirk wasn't really a problem at the moment, but the Vulcan would be able to see right through the perception filter and McCoy knew his staff like the back of his hand. 'Borrowed' uniform or not, one casual glance from Spock would send this whole thing tumbling down.

Striving for silence, but only getting quiet, the Doctor moved towards the door. Spock instantly looked up as he sensed movement and the Doctor smiled sheepishly, he checked to see how close he was to the door, and grabbed a random tool (which would later turn out to be a stylus) and held it up. "Right, just need to get…this"-here he waved the stylus-"and now I'll go do… things. Sorry to bother you, don't mind me. Bye" this said, he whipped around and did what he did best, he ran. There were days when he could come up with the best excuses, and then there were days when he "needed stuff to do things." The Time Lord thought self-depreciatingly.

Behind him, Spock's commanding tone ordered him to stop, and the Vulcan was thoroughly ignored in favor of running faster. The Time Lord reflexively brought the stylus to bear as he reached a turbo lift, waving it frantically up and down the doors. Once he realized what he was doing however, he tossed it away as though it had personally offended him (which it kind of had, it was useless as wood) and pulled out the actual screwdriver.

The turbo lift opened before he could do anything, and deposited a security team bristling with weapons (phasers, they were called phasers). The Doctor grimaced and skidded to a stop, disliking the guns, especially when pointed at him. The team seemed surprised to find him right there, practically waiting for them, but refused to be caught off guard. Rather inconvenient that, he could have used them surprised, much less likely to have good aim then…

The Time Lord, rather than trying to force his way through the crewmembers, turned around and ran back the way he came. Unfortunately for him, Spock and Kirk were already catching up so he was forced down a side corridor. The last thing he needed right now was to be caught, especially if they had phasers, even on stun they were annoying and gave him horrible headaches whenever he was hit with one.

However, it seemed the stylus would have its revenge as the Time Lord, at a full run, trustingly placed his foot where solid ground ought to have been. Except there wasn't solid ground, there was a rather slidey stylus out for revenge. The Time Lord took a rather disgraceful tumble, his momentum causing him to roll a fair way down the hall where he lay winded. The two groups of Enterprise crewmembers arrived shortly after, their phasers pointed unwaveringly at his exposed chest. The Time Lord took the only option available to him, weakly raising his hands in surrender while still trying to catch his breath. "You really shouldn't leave things lying around, someone could trip." He chided, none of them looked amused, so he decided to lay off the comments for now "I surrender, just don't-" he began, but before he could finish his sentence, the Vulcan's phaser went off, directly into his first heart. There was the tingling numbness of a stun blast and he could already feel a headache beginning to form (and this one promised to be a doozy) and then everything went black

Part Three: the best laid plans of Time Lords, men, and homicidal aliens often go awry

Sometime later, perhaps hours, or even days, the Doctor stirred the Time Lord groaned as his brain made a valiant effort to escape his head. The seeming unholy brightness of his surroundings made the man want to curse aloud, in a vain effort to shield his eyes, the Time Lord pulled an arm over his forehead. He drew in a deep breath, trying to focus on getting rid of the headache and get a look at his surroundings.

"Awake I see," a voice taunted somewhere behind him. The Doctor fully opened his eyes, ignoring the pain this action caused, and rolled to his feet. On the other side of the barrier, stood a red shirted man, rather inconspicuous, seemingly just another member of the crew. The Doctor's intuition said otherwise. In fact he was 89% certain that this was the one he had been looking for.

"You're-"he began only to be cut off by the crewman waving his hand.

"Yes, yes, I'm the big bad monster in the shadows, congratulations, you've figured it out." The being said sarcastically, clapping slowly. "And I'm sure you're about to go into some impressive speech about how I won't get away with this and bla bla bla, but to use an old cliché, I already have."

The Doctor remained silent, trying to ponder out the motivation behind this. The Skin-Walker had to know it couldn't kill him here, not without raising questions, so what was the point of being here? "You can't kill me" he said confidently, certain the being already knew this. The exasperated look the Skin-Walker shot him confirmed this.

"Of course not, it would raise far too many questions, however, I am in need of a new host…" It trailed off, looking at him contemplatively.

"You know it won't work. Time Lords have always been immune to your kind." The Doctor countered. The Skin-Walker smirked.

"Not where I was going with that. You see, I need these bozos off my tail, and what better way to convince them to stop looking than for them to think they've already caught the monster?" Almost casually, the Skin Walker hit the borrowed com. "Ensign Winchester to the bridge, the prisoner is awa- Oh GOD! SOMEONE HELP! AH!" An instant too late, the Doctor realized what the Skin-Walker was planning.

The crewmember's chest warped obscenely, pushing out as though something were trying to escape. And it was, with a sickening squelch, the true form of the Skin-Walker emerged in the form of a semi-solid black cloud. The smoke like substance formed a thin hunchbacked form, needle sharp teeth and blank white eyes smiled at the captive Time Lord. It wave a three fingered hand (each finger had a claw that had to be at least four inches long adorning it) and disappeared into the shadows.

"Ensign? Ensign!" came a worried voice from the com. link. Swallowing nervously, the Doctor waited for security to come into the room and find him with the admittedly incriminating body.