There was total stillness in the crystal cavern for several minutes. Sunset stared at the newly carved hole in the ceiling with disbelief, her jaw hanging open.
Sterling Armor slowly pushed himself to a sitting position, raising a hoof to his head to ease the pounding pain. He looked around, locking his gaze on Sunset.
"Sunny... no, SunSET," he thought to himself. He pushed his hind-legs to a standing position, then sat down again, shaking his head slowly. "Sunset Shimmer," he said weakly, trying to maintain his composure. "What... what did you do?"
Sunset didn't even look down. She spoke automatically, her voice far away. "That had to be fifty meters of magic-resistant crystal... she didn't even blink."
There was a moan from near the wall as Stratosphere began to come around. "Ooh man... did anypony get the number of that airship?"
Sterling tried to collect his thoughts. "This unicorn definitely did something... she assaulted me and, almost certainly, that was the Princess of the Sun. She aided a known enemy of the Crown." He looked up at the ceiling, "The Queen may be in trouble. But I feel so weak... I don't think I can teleport to the castle."
He turned his head over towards Stratosphere and pushed himself to a standing position, speaking authoritatively. "Corporal Stratosphere! Front and center!"
Sunset snapped her attention down to the Captain as Stratosphere shook his own head, throwing himself into the air and winging his way over, landing sharply and saluting. "Yes, sir!" He wobbled a little and raised a hoof to rub at a lump on his forehead. "Oooh, man... my head..."
Sterling ignored him and looked towards Sunset, speaking sternly. "Based on what I have seen here, Sunset Shimmer, I hereby place you under arrest. You will submit yourself to the custody of myself and Corporal Stratosphere. We will escort you back to Canterlot and place you in a cell until such time as Nightmare Moon is ready to attend to you. Any attempt to escape custody will result in an escalation of your status and you will be hunted with extreme prejudice."
His eyes narrowed and he met Sunset's gaze. "Is that understood?"
Stratosphere shook his head, "Oh, Sunny. Look what you've done."
Sunset frowned and looked back up at the hole again. "I don't know what I've done..." she replied. Her attention turned back to Sterling again. "Yes... I need to go with you. I don't know what happened to Celestia, but we need to find out as quickly as possible."
Sterling frowned, "What was the spell you cast? What did you do?"
Sunset sighed softly and turned her head. "It was Nightmare Moon's transformation spell. I only needed an energy source... I was going to use the Elements of Harmony, but when I saw you wearing the Alicorn Amulet, I realized I could probably use that. Since you had found us, it was worth a try anyway..."
The blood drained out of Sterling's face, while Stratosphere's jaw dropped. Sterling spoke first, "What did you say the spell was?"
Sunset wouldn't look back to him. "Nightmare Moon's transformation spell," she repeated. "Or at least, the power transfer portion of it. I couldn't have managed the whole thing."
"That... that's impossible," whispered Sterling. "Isn't it? How could you even know that spell?"
"Something went wrong," added Sunset. "It should only have restored her magic. I made things worse... again."
Sterling raised a hoof to his throat, and touched the unusually cool metal of the amulet there. "And you used the Alicorn Amulet to power it...?"
Sunset nodded, her ears folding to her head as she looked away from Sterling.
Sterling cursed and tore the amulet from around his throat, throwing it across the cavern. "Damn this amulet!"
Sunset jumped, startled by the outburst. "Are you all right?"
"It's all my fault," grumbled Sterling. "I should never have worn it; I knew it was the wrong thing to do. If I'd had it destroyed as I had first intended, the Queen wouldn't be in danger."
Sunset frowned and looked in the direction Sterling had thrown the amulet. "We might still need that," she warned. "We can analyze it once we've rested to see how it used to work."
"It's drained," explained Sterling. "I could no longer hear it nor feel its power."
"We can still analyze it," insisted Sunset. "It may be important to understanding what went wrong. We should... we should take it to Nightmare Moon. I'm in over my head."
"You can say that again," Sterling grumbled. He nodded to Stratosphere. "Corporal, retrieve the amulet and bring it back to me." When he had it back, he placed it into his saddlebag. "Where will Celestia have gone?"
Sunset shook her head. "The only place I can think of is the castle."
Sterling frowned, his mind working quickly. He made a decision and nodded quickly. "We need to reach Nightmare Moon as quickly as possible. You need to explain what you did so that we can make preparations to defend the Capital."
"Are you okay to teleport, Sir?" asked Stratosphere. "I can fly quickly, but I can't carry either of you."
Sterling shook his head. "I don't have the magic. I hate to ask this of a prisoner, but Sunset Shimmer: your cooperation will buy you a great deal of good will, possibly even your life. Will you teleport us closer to the castle?"
Sunset frowned and shook her head. "I can't either... not that far. Reflecting that much magic nearly burned me out."
Sterling stomped a hoof. "Then we are going to run. You will keep up," he ordered. His head flipped up towards Stratosphere. "Fly ahead, attempt to gain us access through the shield. Warn the Queen what is coming, and then report to Sergeant Impulse and have him muster the troops. We should not be too far behind."
Stratosphere saluted and was in the air in an instant, turning and dashing up the tunnel they had entered from.
"You," continued Sterling to Sunset. "Is there another exit we can use that is better suited to hoof?"
Sunset frowned, "We can't possibly beat her on the ground... even your air jockey doesn't have much chance of getting there first."
Sterling lowered his horn to her. "That isn't your concern. Is there another exit?"
Sunset considered for a moment. "There's another exit, but we'll have to wink about fifty meters across a pit. Can you manage that?"
Sterling frowned. "We're going to find out. Start moving. Double time!"
Sunset turned helplessly and started up the tunnel. Sterling followed closely, his head lowered and his horn pointing directly at her. Sunset navigated the tunnels at a brisk trot, but at last she called back over her shoulder.
"You can put that thing away," she grumbled. "I'm not going to run off."
Sterling frowned, "Just keep moving." His horn lit faintly to reinforce his point.
"You don't have much magic left," Sunset reminded him as she turned another corner. "Don't be wasting it now."
Sterling grunted, but his horn faded out. They turned a final corner and stood before the deep pit of the ancient mine. Sunset pointed across to the ledge on the far side. "We have to go there," she said. "Can you make it?"
Sterling looked across and briefly lit his horn, only to have it flicker out. He frowned anew and shook his head. "I don't think so..." He looked at the ledge, then back to Sunset.
"I have no choice," he said. "I have to trust you to take this information to Nightmare Moon without me. I will remind you that if you attempt to escape we will hunt you down with extreme prejudice."
"Oh, spare me," grumbled Sunset. "I think I can get us both across. The last thing I want to do is show up in front of Nightmare Moon without SOMEPONY to explain what I'm doing there."
Sterling smirked in spite of himself. "She's got some spunk, I'll give her that. I bet she would have made a good officer." He nodded.
Sunset squinted and focused her magic, her horn lighting up. It took just a moment for her to charge, and then there was a flash of light as the two of them vanished, only to reappear in another flash on the ledge across the cave. Sunset panted softly as her horn faded out.
Sterling looked back across the pit. "Good work," he noted. "Now get moving. Stratosphere must be at the castle by now. We may need to back him up."
"I don't think Celestia is going to be a threat," Sunset said, although she didn't sound very confident. "Even if she was, what are two drained unicorns and a loopy pegasus supposed to do against a fully-charged alicorn?"
"We'll have the full support of the guard by the time we get there," replied Sterling.
Sunset squeezed out of the cave exit and led Sterling through a little grove of trees. She pointed up the street. "The castle's way up there, so it's still going to be quite a run."
Sterling looked up and frowned. "The shield's down," he noted. He lowered his head and started galloping down the street, leaving Sunset caught off guard.
"Hey!" she called. "Well, wait for me! Aren't I your prisoner or something?"
She started into a hard gallop and then gathered the last of her magic to herself and used it to wink alongside Sterling. "Geez," she panted as she kept up. "Don't you ever get tired?"
"Curse that amulet! To Tartarus with the impulse that made me wear it!"
Sunset shook her head as they turned a corner and started up the steep path to the castle. "Curse these hills, you mean."
"You should report to the prison," replied Sterling without turning his head. "This is likely to be no place for a civilian."
"Hey," panted Sunset. "I'm not just any civilian, I'm public enemy number one, remember?"
They both looked up as a squad of pegasi raced towards the castle, and then the lead pony split off and banked down towards them. After a moment they both recognized Stratosphere, who glided above them as they ran.
"Sir," reported Stratosphere, "It's not good, sir!"
Sterling didn't break stride, though he lowered his head further in an effort to push on harder. "Report!" he ordered.
"There's been an attack. The tower's been damaged and Nightmare Moon is... well, sir you'll have to see for yourself. Ulfrid is with her."
"The wolf? Where was he during the attack?"
"I dunno, sir. But he told me to get the air patrols in place and the Earth ponies on guard, then come escort you the rest of the way."
"And Nightmare Moon... is she badly injured?"
Stratosphere looked confused. "She's not... well, that is, I think she's okay, dude, but... you'll just have to see. I can't explain it."
Sterling frowned. "Very well. Please escort Miss Sunset Shimmer to the prison and see that she's secured before you return to the tower."
Sunset frowned. "No way!" she shouted. "I can help fix this!"
"I think she needs to come, dude. Ulfrid said to bring her..."
"The wolf does not run security in this country, Corporal!"
"I know, dude... sorry, sir. But the Queen told me to set up whatever he said..."
"I hate that wolf," Sterling grumbled under his breath. "Very well," he added, louder. "You heard him, Ms Shimmer, faster now!" With that he increased his gallop and pulled ahead a length.
"You have GOT to be kidding me," grumbled Sunset.
They turned the last corner and barreled down the last street to the tower. Ahead of them, they saw an entire legion of pony guard blocking the road nearest the castle. As they drew nearer, they heard a gruff pony shouting, "Make way! Let the Captain through!" A narrow path between the ponies opened up.
"Thank you Sergeant," said Sterling as he raced past, nodding to acknowledge the Sergeant's salute. He entered the tower and ran up the stairs, with Sunset following close behind.
At the top of the tower he was stunned to note that the door was missing and the rock crumbled where the frame once stood. He barged into the room, but still remembered to drop into a bow as soon as he did. "Your Highness," he said. "We got here as quickly as we could."
He heard Sunset gasp behind him as she entered the room, then lifted his head as he heard the deep boom of Ulfrid's voice.
"Captain Sterling Honor, Sunset Shimmer. Thank you both for coming."
Sterling gasped himself as he looked around the room. The walls were scorched and not only the door frame, but the exit to the balcony and the windows all looked as if stone had been blown outwards. Pieces of Nightmare Moon's armor lay scattered about the room, some still smoking lightly. Ulfrid sat near one edge of the room, near a lightly charred cushion that was once a deep royal purple. The wolf turned his head and looked down into the cushion, after a moment a deep blue alicorn sat up from it. She was slightly larger than Sterling Honor and her mane was a light azure color. Her eyes were large and uncertain but as her gaze fell upon Sunset Shimmer, they narrowed. After a moment, she climbed off the pillow, standing and showing her crescent moon cutie mark.
"We meet at last, unicorn," said Luna. "It would appear that we have much to talk about."