Night Shade crouched atop the roof of a fancy Canterlot home, silently observing the surroundings through enchanted night-vision binoculars next to Thunder Armor. He was a strong young Bat-pony stallion, strengthened further by intense training, experience, and the shadowy embrace of evening. Thunder had cast muffling spells on themselves, as an operation like this can be foiled by a single hoofstep or wing-beat. While waiting for their intended target given from local guard reports, Thunder was beginning to get restless.
"I wonder when we'll see-
"-Target spotted." Shade interrupted, at the sight of a suspected Changeling spy.
"Finally." Thunder said with relief.
"Alright. Take that route up through the alleyways. I'll follow above, signaling where he's heading. Keep weapons and spells at the ready. Avoid contact, only use them if things go south." Said Night Shade, with concise and practiced instruction.
He outranked Thunder Armor in the Special Task Force, which was in truth a joint branch of the Guard despite Shade belonging to Luna's authority. Thus, Shade was Thunder's superior. Sometimes this bothered Thunder, because they were close in age. But, he did acknowledge that Night Shade had accomplished more. In fact, due to a certain incident while in direct service to Princess Luna, he was put through the Special Task Force's training program and transferred. The details of this particular incident are confidential.
"Yes, sir." Said Thunder obediently. He levitated his grappling hook off his belt, attached the hook to a solid ornamental statue, and rappelled down the side of the impressive Canterlot home.
Thunder moved contrary to his name through the surprisingly clean alleys, following his target. An occasional glance upwards towards Shade would reassure him that he was still properly tracking their target, which, if it was in fact a Changeling, looked very convincing. It appeared to be a grey earth pony stallion with a top hat, bow tie, and monocle. He was making his way through the dark and quiet streets towards the west gate.
Towards the direction of the caverns, Thunder mentally noted.
Continuing his pursuit, which required swift, quiet movements and occasionally refreshing his muffle spell, his black pull-over mask concealing the light from his horn. He eventually overtook his target and saw the Changeling's approach. With a glance towards Night Shade, who had found cover and rest on a nearby cloud, Thunder waited hidden behind shiny metal garbage cans to make the next move.
Alright, he's almost out of the city. This is confirming every suspicion... Thunder Armor thought, while waiting for the Changeling to pass by. But then, he noticed the way to the west gate becoming busier. And busier. Something wasn't right. More and more high-class "ponies" were making their way onto the street. Two, then four, then ten. Then twenty. And more, And more! Thunder remained calm, and wondered if he should get a better hiding place... He looked toward Night Shade, who used the universal sign for "GET THE BUCK OUT OF THERE." Good, they weren't going to abort. Thunder Armor examined the alley he'd ended up in. There was some old boxes and a dumpster. He was about a block from the gate itself, and needed to move. More and more "ponies" seemed to be coming out of the darkness itself, and he was paranoid that there was... Oh, no. There was. Thunder barely had to turn when he saw them. Coming up from the alley behind him, there were several pony-shaped figures coming towards his direction. He had to move. Now. He didn't dare risk a fight, if it got too noisy all Tartarus would break loose. With Cerberus.
They hadn't yet noticed him, they seemed rather intent on reaching the street. Thunder decided his best way out was up, but that risked drawing attention...
He resented the next thought he had: The dumpster behind me. Yuck.
Thankfully, the left-hoof lid was open, and so slipping into it unseen was easy. The smell, however... For the sake of the reader, let's not go there.
Thunder Armor waited for them to pass, listening. More steps. And more... How many are there? Thunder thought, growing tired of crouching in garbage. He didn't dare shift positions, if he let a single part of him become visible above the dumpster's top, he'd be found out. Finally, after what felt like an hour, there was silence. No steps. No chatter... All was silent in Canterlot. Thunder crawled out of the dumpster, thankful to be free from it's stench. Well, somewhat. It decided to hang around in his nostrils like that one unwanted visitor.
The streets were quiet. Thunder Armor poked his head around the corner to see towards the west gate. There was nopony. Or Changeling. This was definitely more than a spy ring, this had already become a full-on army, amassed to take over Canterlot. They were gathering.
"Oh, crap! Wher-" Thunder managed, before Night Shade appeared seemingly from nowhere, both answering his question and startling him half to death.
"We need to move. They've left the city, and due to you getting stuck, we need to catch up. But, seeing that there's a crowd, catching up shouldn't be difficult. Come on, soldier." Night Shade said methodically.
"Yes, sir." Was the only appropriate response, and quite frankly, the only thing he could manage.
Dusting himself off and levitating off any spare pieces of garbage still attached, Thunder Armor obeyed orders and followed behind Night Shade in pursuit of the mass of several hundred of what were clearly clones. They were following at full gallop, muffled by magic.
Keeping to shadows and foliage, they eventually caught up and they observed the doppelgangers were heading single-file into what appeared to be the entrance to a deep, ancient cavern, the ruins of a long-lost civilization.
"Once they're all in, we follow." said Night Shade.
"Yes, sir." replied Thunder Armor.
Something sinister is just below the surface.