Pinkie Pie hopped along the hallway, opening each and every door to the bedrooms that she could find. Even when nothing interesting jumped out of the room as suspicious, her smile did not waver from her face. So far, she had gone through fifteen different rooms that guests were staying in. She made her way to the sixteenth door, where a Royal Guard stood outside. She widened her smile in greeting, the guard pony unwavering in his stance, and grabbed the handle to the door. Instead of the usual in-out routine, the door did not swing. It didn't even move.
“You won't find anything in there.” said the guard.
“How come it's locked then?” Pinkie's eyes turned to slits, narrowing to the gaze of the guard pony.
“Princess Celestia commands it so.”
“And I command it to be otherwise. I'm a detective. Pip pip.” And with that, the guard reluctantly cast an unlocking spell on the door, the faint click audible throughout the hallway. “Why's it locked in the first place, anyway?”
“Many years ago, when my father was a member of the Royal Guard, Princess Celestia returned from a diplomatic trip to Saddle Arabia with an unknown illness to our doctors. She locked herself in this room for a few months until she recovered. Since then, the room has remained undisturbed.” explained the guard.
Now inside, the room was small, smaller than the usual guest rooms. A single bed sat in the middle of the room, accompanied by a side cabinet and only a side table for furnishings for the entire room. The curtains were drawn part-ways, a single sliver of sunlight flying in through the gap to illuminate the carpet on the floor.
“There's nothing in here. It's been like this for a number of years now.”
“But why seal it off from the world?” queried Pinkie Pie. “All right, I'll need to investigate. You can go now.”
With a bow, the guard pony left, leaving Pinkie Pie to her own devices. As soon as the door closed, she was up and down, left and right, all across the room at once, in a desperate bid to find anything suspicious. A faint buzzing caught her attention a few seconds once she stopped zipping about, a buzzing coming from the window.
“Even in Canterlot, the bees manage to get caught up in the windows. All right, busy bee, I'll let you out. I shall find you with my amazing powers of detection.” Donning her hat in courtesy, she made for the window, fiddling with the curtains and then the latch, humming quietly to herself. But the buzzing grew louder, and closer. Pinkie stopped mid-unlatching and stared at no bee.
Before her, outside the window, hovered a pony shaped being, big green bug eyes staring through the single pane of glass. Fangs were bared, wings were beating rapidly, creating an almighty buzz, bigger than before. Long slender legs had sprouted to double that of a regular pony, and a thick deep black horn glowed a faint green as it's eyes narrowed onto the stunned detective.
“Oh no. Twilight!” was all the pink pony said, before running away from the window and out of the door. The buzzing grew louder still and the sound of smashing glass followed. Pinkie turned around the find the giant Changeling had made it's way through the window, glass littering the carpet. A green blast of magic shot from it's horn, Pinkie doing well to close the door in time before the blast hit her. Keeping her forehooves against the door in case the beast tried to break through, a face of relieve sprawled onto her face as both Twilight Sparkle and Daring Do came running into view at the end of the corridor.
“Twilight!” Another blast of magic was heard, this time breaking through the top section of the door, the spell leaving scorch marks where it had hit. “It's a giant Changeling!”
“What do you mean, a giant Changeling?” asked Twilight.
“I mean, a Changeling that's giant!” shouted Pinkie Pie.
“It's only a silly little insect.” said Daring Do, a look of disbelief on her face.
“When I say giant, I don't mean big, I mean flipping enormous! Look at that blast radius of the spell!” The pair followed Pinkie's hoof pointing to the blast of the second spell. The door towered above them, but even they could see that half of the door could be easily taken out by such a blast.
“Let me see.” Using her own magic, Twilight pulled the remainder of the door open, flinging Pinkie out of the way a bit harshly. She ran in to an empty room.
“It's gone. Buzzed off.” She turned around to the door, both Daring Do and Pinkie Pie walking in. Twilight turned her attention to the scorch marks at the top of the door, using a spell to examine the traits of the Changeling's magical aura.
“Definitely a Changeling. And giant. Well, many giant insectivorous lifeforms in this world, but none in this area. Question is, what is it doing here?”
“Can we please return to sanity? There's no such thing as a giant Changeling.” pleaded Daring Do.
A blood curdling scream was heard, all ears turning to the broken window. Outside, a pony had fallen, a small statue of Princess Celestia on top of them but broken in two pieces. All three ponies ran.
---
The pony was still breathing by the time the trio had gotten to them. The pony was identified as the guard that had gone to the library to fetch the professor, ultimately finding the professor dead at the scene. With great difficulty, he lifted his head up slightly and very quietly spoke.
“The poor little child.” He passed his final breath soon afterwards, and looked almost asleep. Before anypony could do anything to sort out the mess, they heard a familiar buzzing noise. Looking up from the guard pony, they saw the Changeling hovering a ways away, it's horn glowing a brighter shade of green before fleeing.
“There! It's gone back into the castle!” shouted Twilight. They gave chase, running through the same door as the Changeling. In it's wake, it had left a very obvious trail of destruction, multiple statues and vases having been knocked over due to it's enormous size. Following the trail up the stairs, the ponies now found the Changeling cornered at the end of a door-less hallway.
“Oh, but you are wonderful. Just stop, stop there.” pleaded Twilight. Her tone didn't quell the anger the Changeling was experiencing. Another large blast of green magic was fired, forcing the detectives to move out of the way and giving the Changeling an exit back out the way it came.
“Don't let it get away! Quick, before it reverts back to pony form!” They scrambled to get up, and gave chase once more. Following another trail of destruction, it led them to the sleeping quarters of the party guests. “Where are you? Come on. There's no where to run. Show yourself!”
An out of breath Twilight shouted the instructions out as loud as she could. All of the doors flew open at once, and all of the exalted guests of the party poked their heads out to see what was going on.
“Oh, that's not fair” said a now distraught Twilight.
They had lost the killer.