"The mountains are made of sedimentary rock with large quantities of iron buried inside," Spock said, looking at his tricorder.

"How much iron?"

Spock's eyebrow flew up, "The amount of iron would appear to be half of the entire mountain."

"What?" Kirk asked. "That didn't show up on our scans before we beamed down."

"There must have been some form of interference before we beamed down, entirely different from the one that prevented our communication with the Enterprise once here," Spock said. In spite of how exhausted he seemed, some of his usual enthusiasm for scientific puzzles entered his voice.

"But we didn't detect any interference," Kirk said. "Completely undetectable interference? Selective interference?" Why would the interference change once they were on the planet, suddenly preventing them from beaming up when they'd had no trouble at all beaming down?

"Selective interference, that is not directed by a life form of some kind, is unheard of," Spock said. He allowed himself a small sigh before saying, "But that is what the evidence suggests."

"Is it coming from inside the mountain?" Kirk asked. "That much iron means there's probably something under there. A civilization of some kind? Or something technological, left behind?"

"I can make no further conclusions without more evidence," Spock answered slowly, looking at his tricorder again. Kirk forced himself to be patient; Spock would come up with an answer when he was ready. He always did. In the meantime, he started examining the rock wall, trying to see if there was a hidden entrance. Kirk swallowed, his throat so dry he felt like it was about to crack in two. He was at his limit, he'd drunk the last of the water this morning and it was only midday. They had to find something soon, either a water source or a way to get back to the Enterprise.

As if in response to this train of thought, Kirk started swaying again, grabbing on to the wall in support. "Captain!" Spock came over instantly and helped him to sit down against the wall.

"I'll-" Kirk meant to say he'd be fine, but he couldn't finish the sentence. His head was still swimming, and he was starting to see double. He shook his head and tried to get up, only to fall back into the rock.

"Jim," Spock kept a steady hand on his shoulder. "I can search for a way to contact the Enterprise. You should rest."

"No," Kirk said. "We go together. We made it this far by not separating, we're not going to start now." He knew he was being stubborn, but his condition would only worsen with time. He'd have to stay with Spock if he had any chance.

Spock nodded, "Perhaps that is better. It would be unwise for either of us to be alone in this environment in our current condition." He held out a hand to help Kirk, who smiled weakly and took it. The world was still unsteady, and he nodded in gratitude as Spock kept an arm around his shoulders to keep him standing. Moving together like this was difficult, but Kirk shuddered, or would have if he didn't feel like he was burning in Hell, at the thought of being alone here, even for a few minutes.

They stopped suddenly at a completely nondescript section of wall and Spock started scanning it with his tricorder. "I believe I have found something," he said.

"What is it?" Kirk asked. The wall looked completely blank to him, not even an overhang to keep the sun from beating down on their backs.

"A slight decrease in the amount of iron detectable behind this section of the wall," Spock mused. He pushed against the wall, to no avail. "There is no entranceway visible, but there must be some way of getting inside."

"Spock?" Kirk asked. He knew Spock could turn ideas over in his head for hours for the sheer enjoyment of it, but they didn't have hours.

Looking up, Spock began to explain, "If this is the remnant of a long-dead civilization, there must be some way of getting inside. Judging by the selective interference field, they were likely highly advanced, so the opening mechanism for this entrance might be technological in nature, rather than physical."

"If it is a door."

"It is our best lead so far."

Kirk nodded tiredly, "Right as usual, Mr. Spock. Do you think it might be a sonic lock?"

"That is possible, although we would be unable to test that theory while our communicators are not functioning," Spock answered. "But this civilization was obviously adept at manipulating energy fields like the one that is blocking our communicators. The logical conclusion is that the lock will be based on a similar energy field."

"So how would we replicate this energy field?"

Spock stepped back, contemplating the sheer rock face. "I could modify the phasers to produce an energy field. I have no way of isolating which energy field will be the key without access to the Enterprise's computers, however."

"You can guess, though, right?" Kirk asked.

"I can estimate, and try as many different fields as possible."

"Good. Do that. And, Spock, quickly?"

Spock looked at Kirk and got to work right away. The captain knew they didn't have much time left if they didn't find a way to contact the Enterprise; even Spock weaken far more quickly in this environment now that they'd run out of water. This door into the mountain had to be the key. They wouldn't have any time left if it wasn't.

An hour passed, then two. Spock dutifully modified both phasers to produce an energy field instead of the concentrate beam they were designed for. It was a delicate operation that took time and concentration. Finally, Spock stood up. "I have modified the phasers to produce a wave similar to gamma rays. The effect this has on the entranceway will determine what further modifications I need to make." He shot both phasers at the rock wall. There was no visible effect; the energy field was outside the spectrum of visible light. After holding the shot for thirty seconds, Spock consulted his tricorder. "It appears to have had no effect." Undeterred, he modified it further and tried again.

Kirk watched in fascination. The race that had lived on this planet had learned to manipulate energy fields that were invisible to life as it was currently known. Did that mean the inhabitants of this planet had been so different these fields were visible to them? How had they adapted for this harsh environment? This was all irrelevant, but it gave him something to think about.

After about an hour of trying different forms of energy fields, Spock suddenly pushed against the wall. "What is it?" Kirk asked.

"The last field, on the far end of the spectrum of microwave beams, caused a sharp decrease in the amount of iron behind this rock face."

Kirk's expression grew confused, then he said, "Like a door is opening inside!" He pressed his ear against the rock. If he concentrated hard enough he could almost hear the mechanisms moving, although he knew that it was probably his imagination. He stepped back as he felt the wall start to slide underneath him. He and Spock glanced at each other. They were faced with a dark tunnel, apparently leading down into the depths of the mountain. At that moment, it was the most beautiful sight Kirk had ever seen.

They stepped into the blackness, Kirk hugging the wall for support, Spock keeping a hand on his arm just in case. The air was cool and dark, in sharp contrast to the light they could still see from the entrance as they walked further in.

"We seem to be moving down," Spock said. Kirk was still concentrating on what a relief it was to be out of the sun, but he did notice that they ground was sloping downward. He pulled himself back to the present and started concentrating on his surroundings. He realized quickly that part of his relief was coming from a breeze. An underground breeze?

"The air is…moving," he said to Spock. "A ventilation system?"

"Most likely. Conclusive proof that our information about this planet was incorrect. There was a society here, Jim," Spock answered.

"Where there's a ventilation system, there's other things. Technology, maybe water. Come on, Spock. I have a feeling we're almost out of here."