Twilight's horn glowed like a beacon as she cast about with her magic, seeking the origin point of the enchantment that blanketed Equestria. Thunder hummed a low, steady note, providing the required sound component of the spell. Rarity stood off to the side practicing the disruption spell that, combined with Thunder's singing, would allow her to destroy Cacophony's echoes.
"Just in case," Twilight had said. In case of what, she did not say and the others did not press her.
"It's to the north," Twilight said slowly as she tried to pinpoint it. "Somewhere high up. Really high, like a mountain."
"A mountain to the north?" Fluttershy asked. "That could be anything."
"Not as far north as the Crystal Mountains, I think," Twilight continued. "Closer than that."
Rarity came trotting over. "But darling, all that leaves is Canterlot."
"Right." Twilight's horn stopped glowing, and Thunder stopped his humming. "It's the perfect place for it. It's at the center of Equestria, and up on top of that mountain Cacophony would be able to see just about everything."
"Cacophony's working out of Canterlot?" Rainbow asked. "I think somepony would have noticed."
"Canterlot, or the mountain under it," Twilight mused. "Princess Celestia told me once that there are lots of caves, and practically no one goes in there."
"Canterlot?" Thunder facehoofed. "Buck me, we were just there!"
"Thunder, language!" Rarity scolded him.
"Well, what are we waiting for?" Rainbow asked. "Grab the Elements and let's go!"
"I agree," Applejack said,"time's a wastin'!"
"Right," Twilight said. She opened the case holding the Elements and gave them to their respective bearers. After staring sadly at the Element of Laughter for a moment, she put it into her saddlebag with a silent promise to Pinkie Pie. Her eyes shone with determination as she faced the others. "Let's go."
As soon as they stepped off the train at Canterlot station Twilight cast her finding spell again. She turned slowly on the spot as Thunder hummed, trying to determine exactly where the vague sense she was getting was strongest. After about a minute she stopped and opened her eyes. "Yes, it's below us now. It's definitely coming from somewhere in the mountain."
"So how do we get down there?" Thunder asked.
"There's a way into the caves from the palace," Twilight said. "I tried exploring it once when I was a filly. I, uh, didn't get very far." She blushed slightly. "It was dark."
So, for the second time in two days, the group found themselves walking through Canterlot toward the palace. They were struck again by the strained quiet of the city, and this time there was no performance breaking the silence. Thunder kept glancing around, half-hoping to see a sign of Trixie or Octavia. He really hoped Trixie hadn't left the city already, since he was fully intending to take her up on that offer of meeting up for a drink once this was over.
They reached the palace without incident and were escorted in by a guard. Twilight explained what they had found, and though they did not see Princess Celestia, it seemed that the royal guards held Twilight in almost as high esteem as the princess herself. Within minutes they had been led to the lowest level of the palace to a large steel door. The dust on the floor showed plainly that nopony had been here in quite some time, though the door itself was untouched by rust or dirt. The steel of the door glowed faintly with an enchantment that Thunder suspected was responsible for its good condition.
"This was once used for access to the mines under Canterlot," the guard explained as she cast the spell to unlock it, "but no one's gone down there in centuries. Do you really think Cacophony's been right under our hooves this whole time?"
"It seems that way," Twilight answered. The door unlatched with a loud metallic clank and began to swing open. A rush of stale air assaulted them. "What's in the mines?" Twilight asked. "Is it dangerous to go in there?"
The guard shook her head. "Nothing's in there as far as we know. Just old caves and abandoned equipment."
"Well, there's somethin' down there," Applejack said, "an' we're gonna find out what."
"Elements on, girls," Twilight said as she settled her crown onto her own head. The others followed suit, putting on their necklaces.
"Good luck, Ms. Sparkle, everypony," the guard said with a salute.
The group entered the caves and the door slowly shut behind them with an all-too-final clang.
The combined glow of Rarity's and Twilight's horns lit their way through the caves. Twilight was once again casting her finding spell with Thunder's help, while Rarity was shining her light ahead of them so that they could see where they were going.
"Why in Equestria would they have abandoned these mines?" Rarity asked as she swung her head around. "There are still loads of gems here."
"Once Canterlot started to expand the ponies didn't want mining operations happening right under their hooves," Twilight explained. "For one thing it was very noisy, and for another they were worried that an accident could cause a landslide and destroy the city."
Thunder had always thought it was pretty stupid to perch a city on the edge of a mountain like that, but of necessity he kept his thoughts to himself and continued humming.
Twilight's head suddenly snapped around to face down a passage to their right. Mine cart tracks led down into the darkness, but they could not see anything else.
"What is it?" Rainbow asked.
"Something's interfering with my finding spell," Twilight said. She gritted her teeth and forced more power through her horn. "It's trying to disrupt the magic. I think it's coming from this way." She winced as her horn flared wildly, but she managed to bring the spell back under control. Sweat poured down her face as she grappled with whatever was resisting her. Thunder felt the strain as well, and tried to fight back by increasing the volume of the sound he was making.
"You alright, Twi?" a concerned Applejack asked.
"Yeah," Twilight grunted, "just need to break through this resistance."
"Come on, Twilight," Rainbow cheered her on, "you're the most magical unicorn in Equestria, you can do it!"
Twilight winced and closed her eyes, pouring everything she had into overcoming the counterspell. Thunder trembled on his hooves. Finally, with a gasp, Twilight collapsed to the ground and her horn went dark. Thunder stumbled as he felt a sudden release of pressure, but remained standing.
"Twilight!" Fluttershy darted forward and checked her over. Rarity stepped forward to provide more light for the pegasus.
Twilight groaned. "I'm alright, just tired. I should have known better. Cacophony has the power of dozens of ponies, including a lot of unicorns. It's stronger than I am." She massaged her aching head with a hoof.
"Should we go back?" Fluttershy asked. "We can try again when you're feeling better."
"No. No, I'm fine." Twilight forced herself up. "Ponies are counting on us."
"So, no finding spell?" Rainbow asked. "How are we supposed to, you know, find it?
"It came from that way," Twilight gestured down the path she had been looking at earlier. "Beyond that, I guess we'll have to look the old-fashioned way."
As they walked down the tunnel, Thunder's ears perked up. "Do you hear that?"
The others looked around in confusion and shook their heads.
"It's really low, almost too low to hear." Thunder pressed his ear to the wall. He doubted he would have even noticed it if he weren't so used to listening to heavy basslines. "I think it's coming from up ahead, but it's hard to tell in here."
"Let's keep going, then." Twilight was still rubbing her head, but her horn's glow was strong and steady.
The sound grew louder as they progressed. Soon the others became aware of it as well, though it was more felt than heard, a constant rumbling that seemed to vibrate through their legs and chests. Thunder swiveled his ears, trying to determine the source of the noise.
"That way." He pointed down another side passage. When they reached the end of that they found themselves in what looked like a central hub of sorts. Rusted, abandoned equipment littered the ground and walls, and tracks stretched off into the darkness down several different tunnels. Where they stood now was more open than anyplace they had seen inside the mountain thus far, stretching several feet above their heads and wide enough for the entire group to walk side-by-side with room to spare. The low rumbling sound was becoming unpleasantly loud, and Thunder flattened his ears against his head to block some of it out.
"I think we'd better put our earplugs in now," he shouted to be heard over the sound. The others couldn't understand him, so he held up his earplugs pointedly and put them in. The others nodded, remembering that they had brought them along for just such a possibility, and put in their own. Though they still could not hear one another speak, blocking out that awful sound was a relief.
Reduced to communicating by pointing and gesturing, the group attempted to find where the sound was loudest and follow it. Thunder gritted his teeth as they progressed, the noise eventually becoming painful even through the earplugs. If they got out of this without some hearing loss, Thunder thought, it would be a miracle.
Rarity's mouth opened wide and she pointed forward with a hoof. Thunder squinted into the dark but could not see what she was looking at. He looked at her with one eyebrow raised questioningly.
Rarity brightened the light from her horn and extended it farther ahead of them, allowing the others to see what had surprised her: an enormous gem, easily twice the size of Thunder Growl, filled the tunnel and blocked their path. Rarity looked enraptured, but Twilight simply stepped forward and tried to move it. It resisted her every attempt to dislodge it from the tunnel. She eventually resorted to a blast from her horn, eliciting a shriek from Rarity that could be heard even over the grinding, thrumming noise that filled the air, but the gem caught Twilight's beam and refracted it harmlessly, allowing it to pass through and strike the wall behind.
Twilight nudged Rarity to get her attention. She pointed to Rarity's cutie mark, then to her horn, then to the gem. Working with gems is your special talent, get that thing out of our way.
Rarity looked horrified at the idea and shook her head emphatically. I will not!
Twilight sighed and levitated the Element of Laughter out of her saddlebag, holding it in front of Rarity's face. Do it for Pinkie Pie.
Rarity stared wide-eyed at the necklace for a moment, then looked at the enormous gem. She closed her eyes for a moment and a tear leaked from the corner of one of them.
She stepped forward and lowered her head, sending a bright blue ray into the gem. This beam did not break apart and pass through the stone, but struck it solidly. She held the spell steady and a large crack appeared in the front facet of the gem. A few moments later the entire stone shattered and fell to the ground in shards. Their path was clear.
Rarity swooned, falling backward onto a red-padded couch that she had pulled from alicorns-knew-where.
Applejack walked over and tapped her lightly, but the distraught unicorn waved her away. Applejack rolled her eyes and picked her up bodily, slinging Rarity across her back and continuing down the hall, her protests going unheard amidst the noise.
Eventually the group came upon a large metal door, similar to the one through which they had left Celestia's palace except that it was completely rusted. Thunder tried the handle but could not budge it. He threw all of his strength against the door but the rusted hinges would not move. He looked back at the others and shook his head.
Twilight hesitantly tried to cast a spell. When the lingering ache in her head did not spike, she proceeded with more confidence. Purple magic covered the group, and with a bright flash they teleported several feet forward, as close as Twilight dared to her estimation of where the other side of the door should be.
Upon reappearing they were immediately blasted by the awful grating, grinding sound, which was much louder on this side of the door. They all pinned their ears down as the noise gave them instant headaches even through the earplugs. Fluttershy fell to the ground and cowered, attempting to bury her head into her forelegs to block it out.
Thunder, the most accustomed to loud noises, lifted his head enough to look forward. His head hurt to the point that he was seeing double, but he squinted and forced the images together. He realized that he was looking at an enormous open space, nearly the size of the entire mountain. They stood on a platform near the top of the room, and Thunder stumbled backward a step as he realized that he was dangerously close to falling. Floating at the center of it was... something. No matter how he blinked or tilted his head, he couldn't make sense of it.
It seemed like a horrible mockery of an equine. The thing was vaguely pony-shaped, but extra legs, heads, wings, and horns sprouted from it in random places and vanished again, while its central mass writhed and shifted constantly. This thing was not black and shadowy like the echoes, but seemed to contain every color imaginable, swirling around and into one another like a maddened rainbow.
A gentle blue glow filled the air and the terrible noise died away somewhat. The ponies sighed in relief. Thunder turned and found Rarity casting a spell.
"It's a little something I use to help block out distractions while I'm working," she explained. While the spell did not block out nearly all of the sound, it was enough that they could hear one another speak.
"Look down there," Thunder nodded toward the center of the room. The others cautiously approached the edge of the platform. Fluttershy gasped and looked away. Rarity and Twilight looked ill, while Applejack simply stared.
"Doesn't seem like it's noticed us," Applejack said.
"Perfect," Rainbow Dash said. "I can swoop right down there and stick the Element of Laughter on it, then we can blast this thing!"
"Just be careful," Twilight warned her as she levitated the Element over. "We don't know what it's capable of."
Rainbow nodded, but the cocky grin didn't leave her face. She hooked a foreleg through the necklace and took off, streaking toward the monstrous thing in a prismatic blur. Even leaving Rarity's spell and being blasted once more by the full force of Cacophony's sound didn't shake her. Her confidence began to falter, however, as she realized two things: first, Cacophony was a lot farther away than she had thought, and second, it was a lot bigger than it had looked. There was no way the Element would fit around its neck. She would be lucky if she could get it around an ankle.
She drew close to the mass and flitted around it, looking for an opening among the constantly sprouting and vanishing extra limbs. She picked her moment carefully, at a time when its right foreleg seemed relatively clear of the disturbing growths, and darted in with the Element outstretched.
Cacophony thrummed, and Rainbow was blasted backward by what seemed to be a solid wall of sound. She barely caught herself in time to avoid crashing into the wall. Rainbow's eyes went wide as Cacophony's ill-defined head swiveled to look down at her.
Rainbow rocketed back up to rejoin her friends. "Uh, guys?" she said as Cacophony began to move, "I think we're in trouble."