"W—What?" Luna said in disbelief as Doctor Whooves explained the bit about her sister. She glanced from one pony to the other, now speechless. Not only was she utterly useless, but Celestia was the one in danger. But though Celestia had expressed concern for her, now the two other ponies in the room were more concerned with the matters at hand. They were the only two who knew what they were doing, and Luna as just in the way. So she sat away from the pair, just outside the light from Celestia's horn, and out of the way.
The Doctor continued. "They're related to Parasprites, so they were lured to their destruction by music... but what kind? It wasn't polka, I know that got ruled out. I don't think it was the Clopamanea, either. Ahhhh, what was it..."
He sighed, frowning again. "Darn, if I could only get at my library. Or my lab. Or even my cart. Just one cloud-crystal. I don't know what to do." He glanced up at the others. "But I will! Just... give me time! I always think of some way out of these situations!"
"Hmm... doctor," Celestia began, turning to address the stallion, "I once read of a species of ant that farmed aphids for honeydew. It appears that the Manasprites are doing the same with the guards for magic. In addition, their current behavior suggests collective consciousness, like the ants, and in that... a queen."
Luna's ears perked at Celestia's theory about the Manasprites. It was entirely plausible, and somehow... it felt right. Luna had surely studied these creatures long ago, along with many other things she couldn't recall. It had just been too long for her to know anything of value.
Celestia turned once more to face the exit farthest from the door which now held the Manasprites at bay. "If memory serves me correctly, there is a large cistern a few levels down which was used to store fresh water in the event of a siege. It is large enough and well protected enough to support a queen and any of her Manasprite attendants."
"We should be able to descend through that door," Celestia said, gesturing towards the exit on the far wall. "We cannot afford to remain here for long, so I suggest we move immediately."
As Celestia mentioned leaving, Luna stood boldly, if a little stiffly. She was scared to go forward, but more afraid to stay trapped here. At least if they were running away, they'd be making some sort of progress. She moved close to the Doctor, though she mostly brought up the rear of the group. Luna saw staying out of the way as her best option, even if she would have felt more comfortable by her sister.
The Doctor nodded, and gave a broad grin. "Now, that sounds like a plan!" He hopped to his hooves, full of energy. "After you, your Highness! Allons-y!"
He sprung to, following after Princess Celestia, pulling out a small screwdriver and fiddling with it thoughtfully. He kept glancing over to Princess Luna, as they went through the various corridors, following Celestia's memory through the deep passages.
As they made their way through passageways and corridors, Luna was a little surprised by the lack of Manasprites. They had been all over before, but now there were none to be seen. Even so, Luna couldn't help shivering as they made their way through the dark and eerie underground of Canterlot Castle. She kept glancing back and fourth, though she could see very little except for directly in front of her.
The passages were dim, sporadically lit only by the cold fluorescence of ever-burning torches and patches of bio-luminescent fungi that clung to the walls like miniature glowing bookshelves. Periodic flares of lavender hue backlit the ponies trotting down the seemingly endless lengths of stone passages, as the princess periodically lit her horn, "feeling" the surrounding aether for familiar reference points. Celestia did her best to keep her uses of the navigation spell short, lest it attract the attention of additional Manasprites.
"You know," The Doctor finally said to Princess Luna, "My library talks about you two a lot." He glanced up at Princess Celestia. "The Library of the Doctors. It might be why you two almost remember me—because my title, that is, the Doctor, isn't unique to me. It's passed on, from pony to pony. We each inherit the previous Doctors' possessions, library, and solemn duty. To seek out the ills of the land, and heal it. I don't remember, offhand, who was Doctor last time you were both alive. Might have been a pegasus, might have been a unicorn."
Ah yes, the Doctors, Celestia mused. Among the myriad ancient societies that kept their hooves on the pulse of Equestria, the Doctors were among the oldest. The smattering of idle chatter between them was strangely comforting, a small island of normalcy in the depths of the catacombs among the whims of the aether.
At the mention of the Library of the Doctors, Luna's ears perked subconsciously. She had been more absorbed in keeping watch, but the mention of it brought her attention strictly upon the Doctor. She felt a pang of knowing, some memory she couldn't place had resurfaced... or rather, the thought of a memory. Something that she knew about, either learned or seen... something about that library...
"I’d contest your familiarity, Doctor, but that would probably reveal more about my age than a mare should properly share." Celestia chuckled, attempting to add a bit of levity to an otherwise grave situation. "Likewise, there are records in the Royal Archives about the Doctors, though I’m sure the historiographers made certain embellishments. Some of the literature reads like a science fiction novel!"
The Doctor chuckled softly at Celestia's comment on the Doctor's tales. "Oh, yes, wholly exaggerated, I am sure," he agreed lightheartedly with Celestia. "Those ridiculous stories about Medusa's at dig sites, or weeping pegasus statues that make you disappear, or delving down into catacombs with the princesses to save some guards from magic eating bugs, are all entirely made-up, I assure you!" He shook his head. "The things some ponies will repeat..."
He looked to Luna. "I know I often feel scared, 'cause I can't do what a pegasus or a unicorn can do. I can't fly, I can't use magic. But I still do my duty. I find my way—not because I have some sort of power, but because it's the right thing to do. And because that gives you strength. You know the words—Loyalty. Laughter. Honesty.—All the good stuff."
But as Whooves turned to her and mentioned being scared, she had to stop herself from retorting, "I'm not scared!" Saying so would completely give her away, especially if she couldn't keep her voice steady. As he spoke the names of three of the Elements, Luna could not help having mixed feelings. They were both a blessing and a curse, helping to defeat the monster Discord, and also another monster that she knew all too well—herself.
"Luna," Celestia said, smiling faintly at the Doctor’s pep talk, "You mustn't lose faith. We're all in this together."
But still... Luna became melancholy and absorbed in her own thoughts for a moment. There was a reason she'd been able to wield her half of the Elements. She was strong enough, good enough to be deemed worthy by the Elements to be their holder. And yet... it hadn't been enough.
The Doctor grinned roguishly. "Right now, my dear Princess of the Night, you have the most potential amongst all of us, here. You have more capacity for growth than either of us. You may surprise yourself, yet."
She was drawn back to reality at the Doctor's last words. "What do you mean by that?" Luna asked. She had a vague idea... Her magic hadn't fully come in since her return, not to mention that much of her memory was a bit fuzzy. And, being that this was a dark place, and she was "Princess of the Night", this should be her area of expertise. In any case, whatever he was thinking was probably totally wrong. How much did he really know about her?
Celestia paused for a moment to allow her sister and the Doctor to catch up. The aether was flowing here, quite rapidly. Celestia’s incorporeal senses told her that the ley lines themselves seemed warped; that all of them were flowing down towards some indeterminate point in space, as if a singularity had opened somewhere in the catacombs.
"This way," she said. "We’re nearly there. Luna... when we arrive, I want you by my side..."
Luna turned to her sister at the mention of her name. "Yes, Celestia." she said obediently. On the front lines wasn't exactly the place she would have chosen, but this wouldn't be her first battle. And if magic was more of a hindrance than a help, her horn would do the trick.