A small platoon of Solar guards stood at attention, their backs facing the exterior wall, as Twilight paced in front in front of them. The princess may have still been fairly new to this whole leading thing, but the expression in her eyes made it clear that she was here for important business, and every guard was in proper, upright position.
"Gentlecolts, I have troubling news. We have reason to believe that the changelings have infiltrated the Guard," she began.
The guards stood stoically, as if they hadn't heard; though a few couldn't suppress scowls or eye twitches.
Twilight continued. "Therefore, there will be a test, in an attempt to expose them. Every guard must submit to this test, upon pain of discharge."
The guards didn't react to this, either.
"It will be a rather intensive test. But then again, I expect only the best of the Canterlot Guard."
A tiny flicker of pride might have flickered over a couple of faces.
Twilight exhaled. "We have received intelligence that the changelings are preparing another attack, and it is of the utmost importance that we are prepared."
One guard licked his lips nervously.
"After all, upon your shoulders rides the safety of not only our regents Princesses Celestia and Luna, but in fact every pony living here in Canterlot and, by extension, all of Equestria."
Another guard's eyes flicked around the room rapidly.
"It is a great responsibility, but I believe I can rest easy tonight, knowing that Canterlot's finest in the Solar Guard are guarding me."
A guard noticeably puffed his chest out a bit. The second guard flinched and his eyes shifted.
"And furthermore, it is imperative that the Guard be on..."
A body-shaking shiver rose up the guard’s back, and he grit his teeth.
Twilight spun and shot a blast of energy at him, knocking the changeling in disguise back and slamming him into the wall. Before he could react, Twilight had cast another spell, this one more of a beam, and with a flash of purple light, the changeling slumped to the ground, no longer disguised.
Twilight raised a hoof and calmed the startled guards. "Relax. This is all under control."
Two Lunar Guards faded into view, chained up the changeling, and faded back into the shadows, dragging the feebly-struggling changeling behind them.
Twilight turned to the assembled guards. "That was our test. Thank you for your participation. Go to the east ballroom and remain there until further instruction."
The guards saluted and filed out, many noticeably shaken that there had been a changeling in their midst.
Twilight waited until the last guard had left before slumping over, breathing hard. That had been stressful. There was only so much she could do to stall for time; thinking on her hooves was not her strongest quality. She wiped her brow, only now realizing how drained she felt. Still, Twilight was glad she’d figured out how to get a reaction (even if it had been somewhat unintentional). While the Lunar guard had all passed the test without incident, this had been Solar guard changeling number seven already, and this was only the fifth squadron. Who knew how many more there were?
She walked over to the window and looked down through the purple bubble at her brother and his wife. "Good news. We got another one!" she called.
Shining Armor lay on his back, tongue lolling out of his mouth. Like his name, his body was shining; but that was only because he was covered in sweat and various other bodily fluids (at least, what part of him was visible under the blanket they had demanded for privacy purposes). Cadence had slightly better poise as she was sitting up as regally as she could; but this effort was ruined by the fact that she was having a little trouble keeping her body steady, her eyes seemed to be unfocused, and she was also soaked in various liquids with her sweaty mane resembling more a ruined pink haystack than anything else.
Shining caught sight of his sister and cocked his head.
"Oh, right," Twilight blushed. "Soundproof bubble." She lit her horn and cancelled the bubble. "We got another live one! That makes seven in all!"
Shining nodded shakily. “Great. I'm happy for you. Really, I am. But as much as I'm… enjoying this… could you maybe give us a couple minutes to recover before the next squad? Please?”
Twilight averted her eyes, and not just because of the musky scent that rose up from the balcony. "Sorry! One more platoon and then lunch break. Promise."
Cadence nodded hesitantly. "Good, because I can already tell that I won't be walking comfortably anywhere for a couple of days."
Shining smiled weakly before turning back towards Twilight. “Are you sure there was no other option?” he asked. “I mean, it's not like I'm complaining or anything, but I’m kindof… complaining. And I’m exhausted.” He was starting to regret taking Cadence up on her offer of a good time in a closet near the dungeon. Apparently, both Bruch and the other changeling had had a reaction to Cadence’s climax. That had been awkwardness all around.
“And I’m not?” Cadence jabbed playfully, slumping over and resting her head on Shining’s heaving chest. She set a hoof on his stomach and looked up, giving him a gentle smile. “At least I’m just tired and not disappointed.”
Shining grinned and brought up a shaky hoof to gently stroke her mane, earning a quiet nicker of contentment from her.
Twilight coughed uncomfortably. “Yes, well… I didn’t have time to test if any other ponies’ copulation would have the same result.”
Cadence and Shining Armor shared a knowing (if somewhat exasperated) look. She would turn sex into a science project.
Her voice trailed off. “And I didn’t have… anypony else to ask. So it wasn’t even really a test, more of an accident that you happened to be… yeah… there in the dungeon. But still. It got a reaction!” she finished brightly.
“They’re not the only ones getting a reaction,” Cadence said cheekily, nudging Shining Armor.
Shining pointedly pretended to be too exhausted to reply.
“Thanks so much again,” Twilight said as she turned to leave. “Ten minute breather and then the next platoon comes in, so get ready.”
Shining Armor’s jaw dropped as she pulled the soundproof bubble back up. “Ten minu-?! She’s obviously never had sex before,” Shining Armor complained. "This was not in the fine print of our marriage agreement."
He was joking, of course. Their agreement had been oral, and had consisted of both parties promising to love, cherish, and comfort the other, and to make the other laugh daily*. Cadence nuzzled his side gently. “You’re doing great. You’re pleasing your princess—which was in our agreement—and that’s what counts.”
“Which one?” Shining teased. "I've got a couple princesses in my life now."
Cadence jabbed him with her horn. “Hey now,” she protested. "I'd better be your top priority."
Shining grinned and pawed at Cadence's cutie mark. “Trust me. You on top is fine by me.”
Back up in the testing room, Twilight paused. She was vaguely certain she had heard the sound of a playful slap.
* * *
Twilight, Luna, and Celestia sat stoically as Bruch, with chains covering his body again, was brought back into the throne room.
"Remove the inhibitor ring," Celestia ordered.
The guard to his left obeyed, grabbing the strap with his mouth and pulling it off.
"Bruch the changeling," Celestia started. "You came to us with an offer to betray your kind to us."
The changeling crinkled his snout, obviously taking mild offense to the 'your kind' part, but otherwise made no motion.
"Owing to the information you provided, we have found no less than twenty changelings infiltrating the ranks of the Solar Guard, some at high ranks. We have not even begun to scan the general population, or even others in the castle."
The changeling nodded.
"We have decided that the invasion is indeed plausible, and that it would be in our best interest to accept your offer."
Bruch smiled, his fangs poking out from his lips. He flared green fire again and there stood the nondescript red stallion. "I am glad to hear it."
"We will be setting up a special task force, led by a squad hoof-picked by captain Shining Armor and led by our own Princess Twilight Sparkle, to perform a counter-operation."
Twilight did a double-take. "Wh-? Me?" She looked at Celestia, who nodded and smiled comfortingly. She spun towards Luna, who gestured onward with a hoof and had a knowing look in her eyes.
"I suggested you," she said with an encouraging smile.
"Bu- me? But..."
“We trust you, Twilight,” Luna said firmly. “You will do well.”
Bruch politely coughed. "Now that that is taken care of, when do we leave?"
Celestia looked at Twilight. "Tonight."
“Toni-? Tonight. Yes. Tonight.” Twilight nodded, hoping she looked more confident than she felt. She'd just had a large responsibility placed on her. Hopefully she could rise to the challenge.