I don't normally do this sort of thing, but... enjoy.
Ash continued to fall around them, but the temperature remained stable.
"Hmph" was Carmine's only reaction to this. It was the terrain that bothered him. The three hooded figures were high above the encampment, but if anyone noticed them, they were exposed on too many sides.
The hope was that the lanky fellow by the campfire didn't have accomplices.
Carmine's superior gave a hand signal and they proceeded closer, to a clear path down the foothill. Was the man below the reason they were directed here, of all places? There were mineral deposits in the area, but nothing noteworthy. Carmine kept his doubts to himself, keeping an ear out for anything unexpected.
One of the three must have kicked a small rock. The path gave it ample opportunity to knock and echo most of the way down.
"Aww, and you were doing so well, Sneaky Sneaky," said the man below. His cackles chilled the three.
So much for stealth.
They rushed down the mountain to the now-empty camp.
"You've come quite a distance, haven't you?"
The voice echoed from no particular direction.
Carmine followed his intuition, edging closer to the man's most likely exit.
"No plantation's going to hold me again."
Carmine froze. This time, it was a whisper, and too close. His hand reached for his belt. "No," whispered the Commander. He would have to handle this without the use of his -
Too much time wasted. Carmine turned and braced himself as the insane man charged. He was prepared to throw the man, but just before making contact, the man dove to the side, stabbing Carmine in the leg. The pain flared, but for the moment, he still had control enough to kick the man in the head, knocking him cold.
The man splayed out by the fire, the spike that was in his other hand now poking out of his forearm.
Carmine dropped to his back, trying to keep pressure on the spike stuck in his thigh.
The other two removed their hoods and examined him. "Just leave it in there for now," the doctor assured him. "We'll patch you up."
The Commander removed a small device from his belt and calmly said, "Spock to Enterprise."
"Enterprise."
"Four to beam up. Two for medical transport."
McCoy could hardly believe it. Togg's recovery was happening so fast, the spike in his leg seemed to be helping.
"I can hardly believe it," he said to Spock, "He's recovering so fast, the spike in his leg seems to be helping!"
Spock gave him a "fascinating," as usual.
"I feel great," chirped Carmine from the bed.
"Well, let's wait a little longer and see," said McCoy.
Spock quoted some Shakespearean words of encouragement. McCoy smiled at this display of good old Earth culture, and turned to leave the room.
He almost made it before Spock started spouting some stupid garbage. "Hey," McCoy interrupted, to no effect.
"Spock!"
What was he doing? Of all the pointless, green-blooded f-
The misshapen lump oozed across the ground toward a light source nearby.
Spock focused on Ensign Togg's biometric readings. They were elevated in all the right places, but not too high. It was as though the readings were staying just outside the realm of suspicion. Doctor McCoy was enthusiastic. Inappropriately so, given the wound's proximity to the femoral artery. Perhaps McCoy felt a need to cling to some measure of victory, regardless of the unknown dangers still present. This cognitive dissonance could prove useful for motivating him in the future.
"Fascinating," he answered in a carefully controlled tone, lest he be accused of condescention.
Did McCoy have no concern for their attacker, now sedated and under heavy restraints? He had scarcely acknowledged the man.
"I feel great," said Ensign Togg. He was eager as ever to return to action. This was his first landing party assignment, and he likely didn't want it considered a failure.
[several paragraphs of speculation on Togg's background and skills omitted]
"Well, let's wait a little longer and see," McCoy said, in quite the understatement.
Togg would be better served by a little more encouragement. Spock quoted from a Shakespeare soliloquoy Togg had performed himself quite admirably on stage at the Academy. It was thematically not the best match for the situation, but would have more than enough personal significance to him to ease his concern.
McCoy began to excuse himself from the room.
On to the next pressing matter. "Captain's log, supplemental, First Officer Spock reporting."
"Hey!" interrupted McCoy as Spock was dating his entry.
"The Enterprise, in an attempt to keep the shuttle Galileo from falling into a dimensional rift, has itself entered an alternate universe. We are surveying a nearby planet for a way to expand the rift enough to return. Captain Kirk is still on the other side."
"Spock!"
"The landing party was attacked by an unknown person, now in sickbay."
"I'll come back when you're done Vulcan around!" huffed McCoy from the door.
A voice from down the hall yelled, "Just svear already!"
Sulu sat at the helm, maintaining orbit, lost in his thoughts. He was never bored, because his inner monologue had an awesome baritone.
Carmine materialized on the surface. The campfire was untouched, if a bIt dimmer. He whipped out his phaser immediately this time. Directives be damned, this was a short trip.
There was supposed to be a sack somewhere down here.
He tensed. There was something new here, a hideous, amoeba-like blob containing bones and other bodily tissue.
"Forget that," said the Captain. "Get that bag, on the double."
Carmine checked the nooks nearby, keeping lines of sight open.
The sack lay hidden in shadow.
"Good," said Kirk. "Are you ready to perform your penance?"
Carmine froze. This felt wrong somehow.
"Do it, and you will have my trust again. Now, and forever."
"Yes, sir!"
He reached into the bag and pulled out a cold metal spike.
"What kind is it?"
"I'm checking now." A quick tricorder scan later, "It's pure iron, sir."
"Go ahead."
Carmine shuddered, but he wouldn't let the Captain down again.
He sat down, raised the spike high, and plunged it into his other leg.
The pain was lessened this time. Behind it came another feeling, a sort of buzzing in his leg. It didn't stop the pain, just made it... not matter somehow.
"Scott to Togg."
Carmine retrieved his communicator.
"Ensign Togg here."
"I got ya what ya asked for. Everything we've got on dilithium. Picked up an interest in geology, have ya?"
Carmine looked over at Kirk, who nodded in approval.
"Yes. Experimental geology."
McCoy injected another dose of sedative. It didn't make any sense. If they were just going to keep him under, why bring him aboard?
"It doesn't make any sense," he said to Spock. "If we're just going to keep him under, why bring him aboard?"
"A protective measure, Doctor. Besides maintaining the Prime Directive, I do have concerns that this man may be extremely dangerous, and contact with him ill-advised."
"Would you... care to explain those concerns?"
"It would be best to locate your other patient first."
Another fool Vulcan theory. Bones knew that if Jim were in charge, he'd allow the patient to be awake and calm, enjoying their hospitality. He could know he was among friends. Perhaps even enjoy a mint julep, with those fresh mint leaves they just restocked, its sweet, refreshing taste like a warm summer day.
"Doctor?" Spock asked, with a raised eyebrow.
McCoy swallowed his saliva and nodded. Speak of the Devil - "Why, here he is right now!"
And so he was, Carmine Togg. He looked just fine. A strong fellow. He wasn't even limping.
"How's he doing?" Carmine asked. That's more like it, thought McCoy, compassion even for the man who attacked him.
"Fine, just fine," said McCoy with a smile.
Carmine thought for a moment, then took a closer look. McCoy was pleasantly surprised. At least someone was interested in the man. Spock was more concerned about the machine showing his vitals.
"I was just about to take care of that wound in his arm. He should be able to -"
The next few moments happened so fast McCoy could barely react. Carmine, for some reason, went right ahead and pulled the spike from the patient's arm. McCoy hurriedly applied pressure to the wound.
He was about to chew the upstart Ensign out something fierce, but noticed something strange.
Spock had grabbed Carmine's arm, holding it in place. The point of the spike, dripping, faced McCoy. On Carmine's face there was no anger or even mild annoyance, just the same calm he had displayed a moment ago.
"I believe, Ensign, the Doctor can handle the situation from here."
Togg placed the spike on a tray.
"I'm sorry," he said, "I just thought we should get the spikes out of him. He'll be better off, right?"
"Indeed," responded Spock. "Resume your duties."
Carmine sheepishly left. McCoy wrapped the wound tightly.
"Come on, Spock. He was just trying to help."
Spock went to the intercom and called security. "Detain Ensign Togg immediately. Set phasers to stun. Do not attempt to capture him alone."
What in blue blazes?
"Now look here, Spock. What's the big idea?"
Spock returned to the patient's side. "Ensign Togg is unusually healthy for his condition, wouldn't you say?"
"Yes, he is, and it's a medical miracle!"
"Unusually healthy - and unnaturally strong."
McCoy frowned at this. Wherever this was going, he didn't like it.
Spock continued, "Are you aware, Doctor, of any other spikes in this man?"
"Why would I think that?"
"Ensign Togg believes there are."
McCoy scanned him. "There's a smaller one. A little - looks like a bronze nail in his shoulder." He dreaded the answer, but - "What's going on here?"
"I intend to find out." Spock placed his fingers across the man's face, closed his eyes, and began that Vulcan hoodoo thing.
After a few seconds, Spock began to shudder, and recoiled.
McCoy frowned. He almost wanted to laugh at this little histrionic magic trick.
"What I heard," said Spock gravely, "Were three words. 'I am Ruin.'"
...
...
Drinks. Now.
"...and you are mine!" continued Ruin, but the entity was now gone. How did he escape so fast?
Scotty beamed down to the surface with Spock and McCoy. "I feel like I missed all the excitement, sir."
"Indeed," replied Spock, "Before Ensign Togg died, but after we removed his spikes, he suggested the entity possessing him wanted him to ignore this." Spock motioned to the blob.
What a hideous beastie this was! It looked like it'd swallow you whole if you got goo close.
McCoy set the unconscious man down by the fire and picked up the two spikes. The original ones this man had rushed them with. "Here goes nothing," he said, and jabbed the spikes into the blob.
It pulled the spikes in, swirling them around. The blob began to pull itself up, forming itself into a man.
"Thank you," said the former blob. "I should not, with my skills, have let my quarry escape."
Without another word, he slung the unconscious man over his shoulder and began to walk off into the darkness.
"Now hang on!" yelled Scotty, "What's all this mean?"
Spock replied, "Whatever it means, Mr. Scott, we have restored the natural order, however strange it might be."
In the sky overhead, the pinhole-sized rift began to expand again.
McCoy pointed. "Look, Spock, a way home. "
Spock pointed to a different section of the sky, where another rift was already open wide. "That is the rift we came through. I suggest we take it before we find out what else may be coming here."
McCoy could hardly believe it. Spock had saved them all. He had to admit, he had complete trust in Spock's abilities.
"I can hardly believe it," said McCoy, "Uhh... I'm gonna go have a drink."
Kirk shrugged at the non-sequitur.
Scotty pressed the intercom. "McCoy here."
"I'm afraid our friend did a wee bit more damage than we thought. One body for pickup."
Scotty went back among the ducts and knelt beside the dead engineer. He had been stabbed through the chest with a dilithium crystal. Scotty shook his head at the madness, the waste. Then he noticed something else.
A sack full of what looked like old railroad ties.
Two hooded figures surveyed the campsite. Whatever struggle had happened here, all involved were gone.
Captain Archer lowered his hood. "Well? Any sign of why we were brought here?"
His companion said, "Nothing, Captain, but... wait, what's my name?"
"Who knows? Nobody watched Enterprise."
They laughed.
And then Inquisitors killed them.
Edit: Removed spoiler tags.
Unless the instability is a new thing for this character, they've learned to live with it for a while. Be sure you understand your character - what are the conflicting urges pulling them in different directions? If they're in a delicate balance, what does that balance depend on in their regular life? How have they learned to do this - what experiences formed this balance? You don't need to explicitly lay this out, and you can imply to whatever degree you want - your character may even be wrong about themselves. If you've created a fully formed person, that will show when you display their point of view.