Just a few changes for the second version but I took the first round of comments to heart and I think it works better. Thanks. Of course, I'm still open to ideas.

It is complete at 4200 words.

My fingers ache as they grind through the layers of hard black dirt that cover the stone, the power of which I can feel pulsing through the cold earth. Inside I’m craving the energy with a desperate emptiness caused by too many years of enforced starvation. It is desperation that wills my raw hands to continue digging while all logic tells me to stop. But logic does not understand hope so I continue to claw at the base of the cave wall.
A sound from behind me clenches my stomach in panic. Feet climbing, scrambling over the rocks. In the darkness I can’t see beyond the mouth of the cave. Preparing for a fight I grab a handful of dirt and put my back to the rock. The figure that appears is silhouetted in the moonlight. She is harmless, my partner for this assignment.

2nd Version:

My fingers ache as they grind through the layers of hard black dirt at the base of the cave wall feeling the power of the stone pulsing beneath the cold earth. The humidity of the cave ignores the coolness of the night and closes in around me as sweat drips stinging into my eyes. I wipe it away quickly never stopping my quest to reach the power. I crave the magical energy with a desperate emptiness caused by too many years of enforced starvation. It is desperation that wills my raw hands to continue digging while the logic of pain tells me to stop. But logic does not understand hope so I continue to claw at the hard packed soil.
A sound from behind me causes my stomach to clench in panic. Feet climbing, scrambling over the rocks. In the darkness I can’t see beyond the mouth of the cave. Preparing for a fight I grab a handful of dirt and put my back to the wall. The figure that appears is silhouetted in the moonlight. She is harmless, my partner for this assignment. Without a word I return to my task. I don’t have to look to know that she is staring at me not comprehending. In the distance I hear the whirring of engines. A trickle of warm liquid along my fingers tells me they are bleeding where the skin has simply ceased to exist. Time is running out.

My fingers ache as they grind through the layers of hard black dirt that cover the stone,I'm with you so far

the power of which I can feel pulsing through the cold earth.At first I wasn't sure what had the power. Maybe it's the "of which" construction. You could just split this sentence like this: "My fingers ache as they grind through the layers of hard black dirt. I feel the power of the stone pulsing beneath the cold earth." Or something...

Inside I’m craving We know that "craving" happens on the inside. This could just be "I crave"

the energy with a desperate emptiness caused by too many years of enforced starvation. It is desperation that wills my raw hands to continue digging while all logic tells me to stop. Why does logic say to stop? The tension you are setting up here (that she is crazy to be doing this) relies on us knowing this.

But logic does not understand hope so I continue to claw at the base of the cave wall.The realization that she's in cave, heck, that she's indoors, was jarring to me. I assumed she was outside because of the dirt.

A sound from behind me clenches my stomach in panic.This metaphor felt strange. It makes it seem like the sound is doing the clenching, when it's the stomach that is clenching in reaction to the sound.

Feet climbing, scrambling over the rocks. In the darkness I can’t see beyond the mouth of the cave. Preparing for a fight I grab a handful of dirt and put my back to the rock. The figure that appears is silhouetted in the moonlight.Ok, now we have some clear tension, a hook? I've forgotten all about that digging stuff, and wonder why it was there distracting...

She is harmless, my partner for this assignment.And, you've defused the tension. The story feels as if it's over now.

As my somewhat obnoxious comments probably tell you, I don't think you set up a clear hook here. I do wonder why she's forced to starve, what the power in the ground is, etc., but you don't give me enough clarity to care about either. This could be an artifact of my distaste for present tense, or it could be the issues I mention above.

Then, that cover the stone feels like the end of the sentence.

The next part of the power pulsing – you TELL us that she feels it. How about showing. I’d really LIKE to know what she’s feeling. That intrigues me and you shut me out. If it’s that obvious, describe, please.

How about a few details to make it more real? Like broken or torn fingernails. Know how it hurts to have dirt jammed up under your nails when you’re digging even in soft dirt? Maybe even a little bleeding if it’s really hard and there are bits of rock from the cave wall.

Right, it would help to know earlier that she’s inside a cave. How deep? Near the entrance or in the darker part? Is it moist and heavy air? Any bat guano around? How about how her knees are hurting/bleeding as she kneels to dig? Or is she sitting? She thirsty yet? A dry mouth? She wipe her sweating forehead with a dirty back of one hand? Is it cold there?

Grab a handful of loose dirt as a weapon? Come on now.

I chose to write in present tense as an experiment, simply to try it out. I do understand that it's a little awkward.

After re-reading my comments about present tense, I have decided that I am a horses a**. I didn't mean to imply that you are stupid, ridiculous, or otherwise by choosing to write a story that way. My comment was a failed attempt to say "I don't personally enjoy reading present tense, so take my comments with a grain of salt."

The humidity of the cave ignores the coolness of the night and closes in around me as sweat drips stinging into my eyes. I wipe it away [quickly]--Cut this never stopping my quest to reach the power. I crave the magical energy with a desperate emptiness caused by too many years of enforced starvation. It is desperation that wills my raw hands to continue digging while the logic of pain tells me to stop. But logic does not understand hope [so I continue to claw at the hard packed soil.]--I would cut this too, it's repetitive.

A sound from behind me causes my stomach to clench in panic. Feet climbing, scrambling over the rocks. In the darkness I can’t see beyond the mouth of the cave. Preparing for a fight I grab a handful of dirt and put my back to the wall. The figure that appears is silhouetted in the moonlight. She is harmless, my partner for this assignment. Without a word I return to my task. I don’t have to look to know that she is staring at me comma not comprehending. In the distance I hear the whirring of engines. A trickle of warm liquid along my fingers tells me they are bleeding [where the skin has simply ceased to exist]--This is implied. Cut.. Time is running out.

But I think you try to do too much in that first sentence with the fingers grinding and the unspecified feeling of the power (pulsing). I’m trying to figure how WHY this bothers me. It isn’t like you can’t have more than one – yeah, That’s it. Are you trying to connect the fingers (which are aching) WITH the feeling (by the fingers or by more of the body?) feeling – unspecified feeling – of the power (vague reference) pulsing? That may be causing part of the problem here.

So are the fingers feeling ache AND the pulsing? To me that seems a bit contradictory. If my fingers are really seriously aching – and your MC’s seem to be – it’s hard to feel a…. Ummm Perhaps if you detail the feeling evoked by the stone as the primary, overriding sensation I might buy this better. It IS the feeling (please, give us at least a hint of what that feeling IS because we all know what aching fingers feels like) of the power (undefined) that is driving her. By putting the finger ache first you’ve sort of diminished the more important sensation.

In the hierarchy of sensations she’s experiencing, the power must be (surely, since it is driving her to the other) primary and deserve first mention, don’t you think?

That make any sense?

On to my next big problem. It is your use of the term “logic.” Logic of pain is slightly better. We know a bit more of the nature of the logic you kept dragging into the first version.

However, why use the term at all?

It is desperation that wills my raw hands to continue digging while pain tells me to stop. But pain does not trump hope so I continue to claw at the hard packed soil.

Nit – now she’s clawing rather than grinding. Do you really want to change methods of excavation in one paragraph?