A/N: Warning: By the end of this, your brain will hurt.

Two more espers were admitted into Sickbay later that day. One had just collapsed, like Tilaran. The other had staggered around, dizzy, for a while before following suit. McCoy and Chapel worked furiously to try and figure out the cause. Brain functions were clearly up, but there was no indication why.

"LeGuir mentioned a humming sound before he passed," McCoy reported at the staff meeting Kirk called. "So it's definitely the same thing. And it sort of fits with the light and the dreams."

"How so?" Kirk asked.

"Captain, it is definitely a mental phenomenon," Spock clarified. "A non-physical light, the more telepathic crewmembers being most affected by something, dreams becoming reality- are all related to the mind. However, it is extremely difficult to pinpoint the origin." He considered something briefly. "We have also been traveling steadily at Warp 2 since leaving the ion storm. Yet the symptoms persist. It is logical to conclude that they are central to this ship, and not a given area."

"Otherwise we would have left it behind us," Kirk finished. His hand fit the table. "I don't need to tell you how to do your jobs, but we need answers. Two crewmen are dead. Several injured. Six are comatose. If you can think of anything then do it, no matter how crazy. After all," he twisted his face into a smile but it came out more like a grimace. "This ship has performed miracles before.

"Dismissed."

McCoy tromped into his quarters later that night. The condition of the four crewman had dropped when the other two were affected, but they were stabilized now, if still unconscious. But there was no reason for them to be. He sighed and ran a hand through his hair. Even investigating a psychic phenomenon, nothing had come up.

He lay down on the bed and let his thoughts wander, considering possibilities. The sedative was next to him; he had no intention of drifting off. However, a door chime interrupted him from his musings.

"Come in."

Spock entered. Of course, McCoy thought. He skipped me last night. He sighed. Really nothing to do about it. Besides, he'd been up for almost 48 hours and was pretty tired.

"Well, don't be a stranger, Spock," he groused, gesturing a chair. "Sit down."

"Thank you, Doctor," he said. McCoy rolled his eyes. So formal. Even at this late hour.

He sighed for a third time and rolled over. "G'night." He closed his eyes and willed himself to sleep. Oh, Lord, this is so awkward, he thought. He could practically feel the Vulcan's eyes on him and stubbornly resisted the urge to peek over his shoulder. He contemplated engaging Spock in a debate, but then again he had already said good-night and that would just probably increase the odd tension. Go to sleep, McCoy commanded himself. Breathe in, breathe out, breathe in, breathe…

The two days catching up with him, McCoy fell asleep.

Spock had decided to view the observing rotation as a scientific study. He was, after all, essentially observing how the senior officers slept. Kirk had a tendency to roll around a lot, leading to Spock waking him up a lot under the presumption he was in a nightmare. Sometimes he hadn't been dreaming at all. Scott, on the other hand, slept sprawled on his stomach and snored like a train. The engineer would occasionally smack his lips and mutter something, but otherwise did not move. Dr. McCoy, he noticed, once fallen asleep, had rolled on his back and tossed a hand over his head. He slept quietly, and didn't move much more after that. Spock lapsed onto an almost-autopilot; he would snap to alertness upon detecting movement. In the meantime, he allowed his brain to continue to work on mental problem.

His attention was brought back to reality when McCoy shifted slightly. Spock noticed his eyes were twitching, indicating REM sleep. And dreaming. He was about to wake him when Spock hesitated. He remembered Jim saying to let him sleep through the good dreams. He watched carefully for any signs that a nightmare was occurring and leaving behind its handiwork. None came. He relaxed marginally, when McCoy suddenly went rigid. There was a sort of whisper-moan and then he started shaking, sweat appearing on his brow.

Enough was enough.

Spock rose swiftly and shook the man's shoulder. "Doctor McCoy," he said. McCoy started tossing his head. Spock shook harder. "Doctor, wake up!"

McCoy's eyes snapped open, blue glazed with fear. And for a moment, just a moment, that terror seemed to increase upon seeing Spock leaning over him. McCoy tore out of bed and Spock's grip on his shoulder and staggered across the opposite side of the room. He was doubled over, clutching his head. His breathing was ragged, but was slowly being controlled. Spock started forward but stopped, remembering that odd added fear when the doctor awoke.

McCoy, meanwhile, was cursing himself. Dammit, his head hurt so much, and naturally Spock in the room had brought back that nightmare…

Get a hold of yerself, he admonished. Don't fall apart in front of him…

So he mastered his breathing, which slowed his racing heart. Spock observed all of this quietly. Finally, McCoy straightened and gave him a weak smile. "Thanks for waking me up," he said. "It was one heck of a nightmare."

"Indeed," Spock said. "Should we go to Sickbay to ascertain your physical status?"

McCoy waved him off. "That won't be necessary; it wasn't a damaging nightmare."

Spock knitted his brow. "How can you know it wouldn't have turned into one?"

"Because," McCoy paused. "It wasn't. I've had it before and it's not… nothing physically threatening happens."

A glint appeared in the Vulcan's eyes. "Doctor, this could prove very beneficial."

"Yeah?" McCoy shifted.

"Yes. If you have had this nightmare before, then we can compare the previous occurrences with this one, and see if anything is different. It may shed light on the cause of the dream manifestations."

"Spock! That's-" Pause. "Well, logical, but-" McCoy had started to pace the room. "But it's not that serious, hell, it's not even a real nightmare; a memory."

"Even better." The doctor stopped for a moment. "We can compare the dream to the actual event." He folded his hands. "What did you dream about?"

McCoy stared at him some more, then resumed pacing. "Spock, it's kind of private…"

"Doctor," Spock broke in. "We are in desperate need of information. The comparison may very well prove crucial. Do you not have six comatose patients in Sickbay? Would you not help them in every way you could?"

The doctor stopped pacing again and shot him a look. Spock ignored it; he knew what cards to play. Then the doctor's face crumpled. "Oh, Christ, Spock," he said, collapsing on the bed. "There's a reason it turned into a nightmare."

Spock sat down on the bed as well, still on the other side. "Perhaps I can help," he said quietly.

McCoy glanced at him, mildly surprised. There was no 'be of assistance' but Spock had actually said 'help'. His head ached for a moment. Lord knew he wanted help, to make the nightmares stopped. They'd decreased over the months, but sometimes still cropped up. This time had been the worst. In that it had been so real. Eventually aspects of the event had faded, sight and some sensation had persisted, but sense of touch, for example had gone. This time it had been like he was reliving the actual event all over again. He could feel Spock's fingers against his face, he could feel that presence in his mind…

McCoy shuddered and looked up. "Alright, Spock," he said calmly, his voice a low, dead, tone. It barely sounded like his own. "It was the forced mind meld."

He could see Spock turning the words over in his head, contemplating the use of the word 'the' versus 'a'. When at last he spoke his voice was uncharacteristically tight. "When did this happen?"

"Back when we were in the Mirror Universe; Jim, Scotty, Uhura and I."

Spock nodded slowly. "Yes." Voice still tight. Then, "My counterpart?"

McCoy swallowed dryly. "Yes."

Spock was silent for a long time. McCoy noticed that his clasped hands were gripping each other so tightly that the knuckles had gone white. That surprised him slightly. It was about the closest had had ever seen the Vulcan betray emotion. Well, willingly, at least. McCoy stayed silent, not at all eager to continue any more than necessary.

"Doctor," Spock said at last. "Are you aware of the… seriousness… of this?"

McCoy frowned. "I know it wasn't right." He shuddered. Somehow that was understating it. "It certainly didn't feel… right." He paused, contemplating. It wasn't a memory he particularly wanted a closer look at. He gave up and looked at Spock.

The Vulcan, meanwhile, was thinking. On the one hand, he was truly amazed that McCoy hadn't been driven insane like other victims of kae'at k'lasa. The doctor seemed to understand that the experience was bad, but didn't grasp its full weight. That was probably a factor. Humans had an uncanny ability to physiologically respond to what they were told to believe. The Placebo Effect was an excellent example. However, he surmised, in the doctor's case it was more similar to a child reading an adult book. They would get the gist of a love story, but completely miss any biochemical undertones. Unless told otherwise, of course. Unless it was explained. McCoy knew the mind-meld was wrong. But he didn't know how wrong, and so treated it lightly (or at least as lightly as was possible). Spock calculated that he might do more harm than good by explaining the full situation.

"It was," he said, choosing his words carefully. "Immensely unethical. And atrocious." He cleared his throat. "I would prefer that we discuss this at a later time, Doctor. Let me clarify: it is very important that we discuss this. However, the current situation calls for something else." He shifted slightly.

"What is it, Spock?" McCoy asked. "You've got that look in your eye."

"We have already established that this is a mental phenomenon." Spock looked him in the eye. "May I conduct a mind-meld, McCoy?"

Initially, McCoy blanched. He was still feeling the after-effects of his nightmare. However, this Spock wasn't forcing him. He'd asked for permission. And that touched McCoy. One of the hardest things he'd had dealing with was how the other Spock had just used him as a tool. He didn't ask, he just got what he needed to know then dragged him back to the transporter room. There was no acknowledgement that McCoy had a life, that he had his own mind, his own thoughts, his privacy, dammit! He was tossed aside the moment Spock was done.

This Spock was asking.

Asking McCoy.

"Yes, Spock," he found himself saying. "Let's see what this is all about."

They sat facing each other on the bed. Spock quickly prepared himself. He was hoping to find some impression of the mental phenomenon, yet also wished to glimpse the doctor's mental state. Because dreams were real to the body, no doubt the nightmare had been the equivalent of a second forced meld. There would definitely have to be healing later. He would just quickly see what would have to be repaired.

He didn't get the chance.

The moment Spock made contact he and the doctor were flooded with a torrent of being. It was staggering, and Spock fought to maintain control in the odd limbo. He sensed McCoy slipping away in the flood and grasped him tightly, grounding him.

Thanks, he felt. Spock also learned, no doubt from sharing the doctor's thoughts, that this was the experience felt when the light had appeared.

It was fascinating. Time did not exist. Nor did space. Yet Spock felt everywhere and nowhere at once. Spock? Names seemed meaningless. There was an increased sense of self-actualization. He was who he was. He felt so connected with others, knowing who they were. They were them. Enlightening was a very accurate word, and he felt McCoy's laughter, (no, sound did not exist yet this whole thing sang, humor was a better word) at the comparison of that word to the light flooding them.

Then they felt something else. Another… consciousness? No, that word seemed to fall short. It was a collection of being; a collection of existence. It joined them in no physical sense, and greeted them without words. Caught up in the sensations, Spock struggled to say, or rather think, 'Hello'. McCoy did the same, albeit with more difficulty.

Hello, the collection answered. Spock was intrigued. Language had suddenly become crisp, and not abstract. Also, it had replied in Vulcan. Though McCoy heard English.

Inquiry, it continued, picking up on their emotions/intent. Spock was utterly fascinated. He had not yet put it into words… what exactly could he inquire about? Yet it seemed to know he was questioning… everything.

There was a delay. Forgive me, it said. Words are very new, and quite odd. Limiting, but a fascinating concept. I am picking up from your minds this 'Language', or, pardon me, these 'Languages'. It is apparently very difficult for you to actively think without these words, if not impossible.

Before Spock could ask a question, it already seemed to know his intent. More inquiry. I could tell you all instantaneously, but judging by how overwhelming this is for the two of you now, I shall have to explain things one at a time. It spoke, if it could honestly be termed that, flawlessly, seamlessly, and completely.

'Could you start with your name?' McCoy's broken thought came through. It pierced the- experience- and seemed abnormally stiff and sharp against the organic unity of everything.

A name, it mused. Spock could honestly not think of how to describe… it. Names are even more abstract than Language. I am Me; that is what I know. However, for your sakes I shall strive to come up with a contemporary title. It paused. Who am I? You could call me Afreel, though it holds no meaning to me. Merely a random collection of letters that I find pleasing and do not form a word in either of your Languages.

'What are you?' Spock asked. His thought was not as one-tracked as McCoy's, yet still seemed to upset the flow of… whatever it was. 'What is this?'

Ah yes, Afreel said. The two go hand in hand. It's a pity I cannot simply inform you in my own way. I shall try to make use of your Languages accurately. Beat. I am thought.

If Spock had an eyebrow visible, it would've risen sky high. Perhaps it was up in his hairline back in the real world.

I am thought, Afreel continued. And this, as best to your understandings, can be described as the Mental Plane.

'Fascinating.' He sensed an underlying of McCoy's thoughts. They were along the lines of how he said the word even in his mind.

I am not alone, Afreel was saying. I am merely one form of thought. It was decided that I would be best to welcome you. We are quite elated with this Contact.

'Contact?'

Yes. There was warmth in Afreel's tone. We grew. We felt. We realized. We learned. And these continue. We are sentience. We eventually learned that there was a form of existence beyond ours. Beyond Mentality. Afreel paused. I shall tell you everything that your knowledge permits.

Occasionally we would feel undercurrents in Existence. Moments of activity that would fade. Often several at once. Moreso none at all. In the lower levels of thought, it was like something was accessing our Existence, this Mentality, briefly every now and then. Like now.

Spock quickly put it together. Of course, the Mental Plane! Those activities were mind-melds and other forms of telepathy in use.

Afreel purred in agreement with his logic. Yes. These clued us in to another plane. There was another form of Existence. You term this as the Physical Plane.

Spock and McCoy were dumbfounded. While McCoy was digesting the information Spock was getting more and more excited. The Universe wasn't the limit; the final frontier. Not even parallel universes (which drew a twinge of emotion from McCoy). Everything- from physics to atoms to biology –was physical. Three-dimensional, two-dimensional, four-dimensional, gravity had some effect of shape, even time! After all, time was measured by the passage of space, which was physical. However, thought wasn't physical. Emotions weren't. States of existence weren't physical, like curiosity. And there was a whole plane dedicated to them.

Yes, Afreel rumbled. Anyways, we grew very excited about this possibility. Space, the idea of form; it's very foreign to us. Nevertheless, we decided to try and make contact with this Plane. Not knowing what to expect, we decided on a trial for the machine we constructed.

'Machine?' McCoy wondered. 'How can you build a machine without any tools? Without anything for that matter!'

There was an impression of Afreel inclining its head. I use the phrase as a metaphor. Like you can make artificial replicates of items around you, we can make artificial thoughts. We constructed a mass of thoughts designed to cross the barrier to the Physical Plane.

'Like equations,' Spock felt sudden insight. 'Equations that do the work instead of merely describe it.'

Rather accurate. Whereas your mathematics explain functions in your physical universe, our- mathematics –are the functions in this mental… universe. We did have a lack of data, however. Again, we previously, before encountering your minds, had no idea of space. Due to the occasional burst of activities along the lower levels of Existence, we gained a rudimentary perception of time. Therefore, after powering up our machine, for lack of a better word, we activated it fully for only a couple of your seconds.

Everything clicked. 'We experienced an ion storm,' Spock thought slowly. "That was incredibly unusual. Followed by an experience much like this.'

'It must have been the effects of powering up your machine and turning it on,' McCoy bubbled excitedly. 'You did make contact!'

Briefly, Afreel calmed. We felt you all. The sudden company alerted us to our success. Yet you all did seem very lost. Extremely lost. So we cut the machine to lowest force and since then have only been minutely increasing it.

If McCoy had physical form he would have been bouncing on his toes. 'We had some more telepathic crewmembers affected by your machine powering up. Then everything was fine until you started increasing the power again. They described a humming, like what's here, and then slipped unconscious.'

Afreel seemed mortified. We have been getting weak signals during the powering up and low settings, it said. Touching on mentality gateways, but not quite getting through. What I mean by mentality gateways are your minds. By thinking, and mainly through telepathy, you access this Mental Plane. However, you can apply these to the physical world. I grieve to think that we are causing harm to some of you. We shall look for a way for the machine to not reach more receptive minds unless on full power used for contact, such as earlier.

'That's not all,' McCoy continued. He transmitted the circumstances of the dreams without coherent words. It seemed to explain the situation clearer to Afreel.

I am sorry that we have caused you trouble… and death. Afreel tested this newest concept. We shall terminate the machine until these problems can be rectified. Its attention shifted to Spock. More inquiry, I see. Why your vessel was affected and not the whole Physical Plane? And why it continues to be affected? I have a very poor concept of space, I'm afraid. I can speculate that the area in which we tested our machine became physical, and your ship was caught in it unintentionally. As to why the machine continues to latch to it, I do not have as easy an answer. Distance is very baffling. I can only assume that since we have not turned the machine completely off, it remains latched to your minds. This manifests your dreams, born from the sub/unconscious, and causing comas to your telepaths. Remember, it was designed to cross from Mental to Physical.

'And our dreams are certainly doing that,' Spock finished. 'Despite any harmful effects, I ask that you do not immediately terminate your machine. It may be more difficult to establish contact afterwards. We wish to continue discussing with you.'

Yes, Afreel replied. I understand your mission of contacting intelligent life. Although I do not suppose we are considered 'Life' by your standards, we are 'Intelligence'. Very well, we shall not turn off our machine, but we shall put it back at its lowest setting; it may help your patients, it addressed McCoy. Its demeanor turned more serious. You have a commanding officer; go to him. Perhaps we can find a common ground, a direction in which to proceed with negotiations, concerning your 'Federation'. When will be good for us? Afreel mulled it over. Time to us is still very abstract, even moreso than to you. We shall adjust the machine as soon as possible. Initiate another… mind-meld… whenever is convenient for you. We will know; we will be waiting.

The Existence flickered. It is time to go, Afreel said, and then suddenly they were back in McCoy's cabin. After getting over the initial shock of having a body again, they looked at each other; as if to be sure what they'd just experience was real.

"Spock," McCoy said, rediscovering his vocal cords. "What on Earth just happened?"

For once, Spock could not find the words for such an event. Instead, he simply rose and said, "We must inform Jim."

Told ya your brain might hurt. Why do all my better ideas about anything have to be so confusing? I tried to phrase it as clear as I could; lemme know if you have any questions about Mental/Physical planes. This is hands-down the longest chapter I've ever written (as so far), so it may be a slight shock for followers after the others numbered less than 2,000 words. Sorry to hit y'all with it, but I did warn you at the top your brain might hurt. All I can say is take an aspirin or something (but I deny saying this, because I'm not a doctor and refuse to practice medicine illegally.)

Please review!