"What even is this?" Twilight asked. "I don't think it's a dagger, or a knife. The blade is far too wide. And it isn't sharpened."
Spike picked it up, and turned it over. He held it in his claws, and pretended to brandish it like a sword. He deflected the saber strike of an imaginary opponent.
"I dunno," he conceded. "But I think I know who might."
***
At Tools & Useless Things, Kerfuffle eyed the object Spike had laid down on the counter. "Of course I do," she said. "It's a trowel."
Spike's eyebrows rose. "It doesn't look like it would hold much dirt. Shouldn't it have...a bit of a curve to it? To help carry the dirt in?"
Kerfuffle smiled. "Not THAT kind of trowel. This is for laying down and smoothing mortar. So it HAS to be straight, or it won't work right. Your bricks wouldn't lay flat. Or your stone blocks, or whatever."
"Huh," Spike said. "That's weird. The one thing Cozy never showed any interest in was manual labor."
Now, Kerfuffle smiled a bit too forcefully. "Ponies can be interested in more than one thing!" she said. "While you're here, would you like to take a look at an impractically long necktie? A fancy, fancy hat? Perhaps a mare in your life would like a bit of fashion, to help her feel as beautiful as she looks?"
"Nah, but thanks," Spike said. "Me and Rarity are super tight. I think I've got my fashion needs covered. Unless you have a sale on fashionable gems that taste good to eat, and don't cost too much?"
In Kerfuffle's imagination, an overgrown lizard grabbed one of her most beautiful clothing designs with its disgusting reptile claws. He gnawed the gems off one by one, leaving only shreds of fabric scattered all over the floor. And he didn't clean up after himself, either.
She gritted her teeth. "No, I seem to be all out of sale items. See you later!" She pushed the young dragon backwards across the floor and out into the street, slamming the door shut behind him.
Kerfuffle sighed. "There's no point in trying to sell my clothing creations in Ponyville. With Rarity living in the same town, nopony can compete." She looked at the neglected, dusty "Couture By Kerfuffle" end of the store, where garments seemed to droop sadly on their hangers.
"What's that, Dress Number Seventeen?" she said. "You're right! I should move to someplace so far away, I'll never have to see Rarity or even hear her name ever again!"
***
After going back to Kerfuffle's store briefly to retrieve the trowel, Spike walked back to the Castle of Friendship, where he found Twilight organizing one of her lists of checklists.
Spike held up the trowel proudly. "I found out what it is! It's a trowel."
Twilight eyed it. "Not a speck of dirt on it. It looks like it's never been used."
"Kerfuffle told me it's for mortar, not for dirt. It's a construction tool."
"Hmm. I wonder why Cozy Glow had something like that."
Spike shrugged. "If it's a mystery...maybe it's a clue too. We still don't know why Cozy Glow was so evil. If she'd destroyed all the magic in Equestria...well, you know how much trouble that would have caused. all the pegasi falling out of the sky...and some of them would have fallen on Earth ponies, too."
Twilight nodded. "So many things would have gone wrong. It seems like literally everything in Equestria would be changed."
With his tough dragon teeth, Spike absent-mindedly chewed the end of the trowel, creasing and wrinkling it. He pulled the tool out of his mouth to say, "That doesn't narrow things down much, does it? It seems like the motive could have been...nearly anything."
Twilight grinned. "Motive! That's a good point, Spike. You're thinking like a real detective!"
"Aw, shucks. I just learned by watching Rarity solve a case, that time when Rainbow Dash was framed for writing a fake letter. And by listening to her talk about her favorite detective novels. And by reading them to her, sometimes, while she sewed." Spike sighed. "You know, back when I used to have a crush on her."
"But it seems like you learned a lot. If YOU investigate the mystery, maybe we'll finally learn the answer. And if we know why she turned out so badly, maybe we can stop other fillies from going bad too."
Spike slightly tilted his head. "Maybe. I guess it's worth a try."
With one forehoof, Twilight clopped him on the shoulder. "I really think you can do it. And if you find out how to prevent the next evil ten year old from doing something terrible that almost destroys the world, you'll be saving the world in advance of the crisis, INSTEAD OF our all waiting until the very last minute and almost getting defeated while Celestia and Luna and I and the Element Bearers all get our snouts ground into the dust! Doesn't that sound like a good idea?"
"Yeah." Spike stood up straight, and took a deep breath. "I'll try it."
"Great! This file folder has all of Cozy Glow's student records. If you need anything more, just let me know."
"Thanks, Twilight!" Spike pushed out his chest proudly. "First, saving the Crystal Empire. Now, saving the world from being destroyed by evil children of the future. I think this being a hero thing could become a regular habit!"
***
Spike heard a familiar voice. "Spike!" it said. "Can you hear me, Spike?"
Spike opened his eyes, and looked around. "Luna? Where are we? What are all these doors for? What's behind them? If I open the wrong door, does a tiger eat me?"
Luna laughed. "Think again, Spike. No tiger can harm us here, I promise you."
Spike's eyes roved farther. "And what are all those glowing lights floating through the air?" Spike blinked. "I think...I've heard about this! I know where this is! A place where it seems like we're just walking on nothing, and there's enough light to see by, but the background far away from us is...a dim blue that seems to go on forever. This is where Twilight went, when she turned into an alicorn!" Spike gasped. "Am I going to be an alicorn? A...dragoncorn? Is that even a thing? Or am I going to be a pony? Will my friends even recognize me?"
Luna snorted. "This is a dream, Spike. Or specifically, the Realm Between Dreams. I pulled you here from your regular dream, because I needed to speak with you."
Spike exhaled. "Huh. What a weird place. So, what do you want to talk about?"
Luna's brow furrowed. "I need to get a message to Twilight Sparkle right away. As soon as you wake up, which should be right after we finish talking, I need you to tell her my message."
"Huh." Spike blinked. "That's going to be tough."
"Why?"
"Because last I remember, when I was awake, I was on a train hundreds of miles from Ponyville, and going even farther. I'm investigating the Cozy Glow case."
Luna's eyes narrowed. "That obnoxious brat who tried to take away all the magic in Equestria? And almost succeeded?"
"Yes. Twilight sent me to find out how she ever got to be so bad." Spike snapped his fingers. "Hey! I have an idea." He closed his eyes (in the Dream Realm, that is. His eyes in the waking world were already closed. So I suppose for a few seconds, his eyes were DOUBLE-closed.)
Spike opened his eyes again, and a trowel was gripped in his claws. "I did it! I can show you the first clue. The teachers at the School of Friendship were going through Cozy's things, and they found this trowel."
"I did not know that Cozy was a gardener. How curious."
Spike shook his head. "Not a gardener, exactly...never mind about that. Oh, and another thing! I already have an idea for how we can prevent another Cozy Glow from stealing all the magic. Again."
Luna sat back on her haunches. "You do? Tell me."
"Cozy Glow learned how to take away Equestria's magic by writing to an evil pen pal, right? So all we have to do is, don't let foals under the age of eighteen send or receive mail. A foal like Cozy Glow won't even be able to get STARTED on her evil plan. Because she won't even be able to ask her pen pal what the evil plan IS." Spike jumped up and down. "Isn't it a great idea?"
"No."
"What do you mean, no?"
"The postal service is very important. We must let little foals send letters to whomever they choose."
"Why?"
Luna said in a very serious tone, "So they can write letters to Crystal Kringhoof."
Spike blew flames out his nose and mouth. "That's ridiculous! Everycreature knows Crystal Kringhoof isn't real. Did you come here into my dreams just to play jokes on me?"
"No, my dear Spike. It is VERY IMPORTANT that ponies of all ages use the Equestrian postal system. They learn so much by exchanging letters with NON-evil pen pals. Also, their letters to Crystal Kringhoof are important sources of information for Foal Protective Services. Every time somefoal writes Crystal asking for a new mommy and daddy, or begging for more gruel--"
"Ok, ok, I get it. Paws off the postal service, and let foals get letters from evil villainous monsters."
Luna nodded. "It really is better this way."
***
One reason Spike had been chosen for this job, he thought, was that he was a naturally winged creature. Just like birds, pegasi, bats, butterflies, moths, and great-winged stinkbugs, he was able to walk around in a pegasus cloud city, without falling through the streets or floors towards the ground far, far below.
In Cloudy Heights, Spike looked for the address listed in Cozy Glow's school records. Knowing what a conniving, dishonest schemer Cozy was, Spike was surprised to find a cloud house at the address. A mare with a family resemblance to Cozy Glow answered the door.
"I don't want any," she said, and slammed the door.
Spike knocked on the door again. "I'm here about Cozy Glow!"
The door reopened. "How is she?" the mare asked.
"She's...not doing all that well, I guess. I've been sent by a princess to ask some questions about her."
The mare's eyes shone. "A princess! I've always wanted to meet a princess. Could you introduce me to the Royal Court?" The mare stuck out a forehoof, which Spike shook. "I'm Greasy Glow, Cozy Glow's mother."
Spike said, "I'm curious what Cozy Glow was like when she was younger."
The mare nodded. "When she was a tiny foal, we had such high hopes for her. We had no idea how much of a problem filly she would become."
***
In the middle of a muddy, dirty construction site (on the ground!) Cozy Glow smiled proudly. "Isn't it neat?"
"So THIS is where you've been sneaking off to!" Cozy's mother said.
"Why are you so upset? I haven't been doing anything wrong!"
"You've been getting...DIRT in your tail! And your mane! At first, being proper high-class pegasi, we didn't even know what it was. But now we know." Greasy Glow gestured at the block wall. "You've been building some kind of...dirt thing! Out of dirty gray blocks, and gray mud to stick them together!" She spat on the ground.
"It's called cement, mom. And cement blocks. It's really neat stuff! You can build almost anything out of them, and they don't fall apart as easily as cloud houses do."
A big pony in overalls said, "Youses daughter is a real good builder. She builds such nice towers. And I don't think I know ANYPONY who does crenellations so good as hers. Youse must be SO PROUD of her. She could go pro."
Cozy's mother slapped the stallion. "Not if I have anything to say about it. Not THIS kind of pro. If she can't be a high end accountant who makes two plus two equal anything she wants it to be, or a lawyer, or a corporate executive..." She slapped the stallion again.
"Hey, lady. I get that this isn't what you expected of your daughter. But if we love our children, we should try to let them do whatever honest work makes them happy--"
The mare slapped the stallion again. "Do NOT say the H-WORD in front of me!"
The stallion blinked. "Whaddaya mean? I didn't say--"
"HONEST WORK! DO NOT SAY THAT IN FRONT OF MY DAUGHTER!" She sniffed. "My daughter is better than that sort of thing."
"But Mommy," Cozy pleaded, "I love building so much! I like it better than anything else in the whole world!"
Cozy Glow's backside shone brightly, as if she was a pony-firefly hybrid. When the glare faded out, her flank was marked with an image of a tower, complete with castle-style crenellations on top.
"Oh, dear Celestia no!" Cozy's mother shouted. She slapped the stallion again.
***
The train rattled as it traveled along the tracks.
Sitting in a passenger car, Cozy Glow asked, "Where are we going, mom?"
"We're going someplace where you'll get the help you need."
"Will I get to build things?"
"After we're done, honey. After we've taken care of this, you'll get to build all the things you want to." The mare said to herself, "Which won't be anything at all, except maybe the most evil kind of corporate empire."
***
Starlight Glimmer ushered the filly and her mother into Starlight's house, and shut the door tightly for privacy. "Now you understand," Starlight said, "some ponies think this kind of work is...morally questionable."
"That's what I like to hear," Cozy's mother said. "Tell me more."
"I read your letter, and I think I can help your daughter."
Greasy Glow wailed, "I've been so worried about her! She's gotten her cutie mark, and it's in...CONSTRUCTION! What kind of pegasus works on the ground, anyway?"
Starlight patted the mare reassuringly. "Don't worry, Missus Greasy. I can help your daughter. I'm the best cutie mark mage in Equestria. All we have to do is, let her keep her cutie mark, but change its MEANING."
Greasy blinked. She wiped her eyes. "You can do that?"
Starlight grinned. "Most unicorns couldn't, not in a million years. But for ME? No problem! I just hope you brought the briefcase."
Greasy put a briefcase on the table.
Starlight opened it, and rummaged through the contents. "Ordinarily," she said, "I would have a highly skilled expert check all this money to make sure it isn't counterfeit. But Our Town seems to be short on highly skilled experts right now. So I'll have to rely on threats." She glared in Greasy's face, and poked her with one forehoof. "If any of this money is fake, and you don't tell me right now, one of the most powerful mages in Equestria is going to be very angry at you. If I can change the meaning of a cutie mark for somepony who I want to help, can you imagine what I can do to somepony I don't like?" She grinned an evil grin, like a villain looking forward to teaching an innocent, naive student to transform all the villain's enemies into teacups and smash them into pieces.
Greasy said, "The bank told me it's real! I swear by Celestia's mane! But if any of it's fake, I'll replace it! I don't want you to be angry at me. I just want you to fix my daughter to be the filly I want her to be!" Greasy bawled. "I'll do anything! Just fix my baby, please!"
Starlight's horn lit up. "I've been thinking about your daughter's case. How about if instead of somepony who stacks blocks, I turn her into...a cunning chessmaster!"
Greasy blinked. "Somepony who plays board games?"
"No! It's a METAPHOR, for a clever strategist who outwits her opponents with tricks and gambits they can't even begin to guess ahead of time! For somepony who uses other ponies as pawns, and ruthlessly discards them, sweeping them off the board!"
Greasy was quiet for a minute. "Well, cunning and ruthless sounds nice."
***
"And would you believe," Greasy Glow complained, "She never writes! It's like she doesn't even care about her own mother."
"Heh heh," Spike laughed nervously. "Are you sure that's what the cult leader was like? In a town by the end of the Appaloosa branch railway, a light purple coat, her mane and tail striped like--"
"And her name was Starlight Glimmer. I'm sure of it." She pursed her lips. "I don't know why you would ever doubt me. I am a VERY careful pony, and I always say exactly what I mean to say."
Spike shrugged. "I guess your story makes sense? But on behalf of the Equestrian government, I have to ask you to make sure we can reach you if we need to ask you any more questions."
"Of course!" Greasy said. "I'm always happy to help our wonderful princesses! You're welcome to stop by anytime, day or night." She put her hooves on his shoulders. "Now, is there anything else I can do for you? Bribes?"
"No, thank you. I'm not allowed to accept bribes anymore, not after the second Greed Growth Incident."
She pushed him towards the door. "I am SO HAPPY I was able to help you with your mystery. Next time you see Cozy Glow, tell that little brat if she gets locked into Tartarus, it's exactly what she deserves!"
"Heh heh. Well, I guess I should be going. Thank you again, Mrs. Greasy Glow."
***
Spike was careful to send a report off to Princess Celestia well before he arrived back in Ponyville. To quote part of the report, "It isn't that I don't TRUST Starlight Glimmer. It's more that I think sometimes she has very poor judgment, and she has a history of making bad decisions."
***
In the School of Friendship's faculty lounge, Spike and Twilight Sparkle sat across a table from Starlight Glimmer. Several other instructors 'just happened' to be in the room, trying not to look like they were ready to subdue the former cult leader if she went berserk.
"So that's what happened," Spike said.
Twilight grimaced at Starlight. "Do you have anything to say for yourself?"
"Oh! Starlight said. "NOW I remember her. When she arrived at the school, I THOUGHT she looked familiar, but I couldn't place her."
Twilight shouted, "You twisted the destiny of a little filly and you couldn't even REMEMBER HER?"
"Hay, I messed with the cutie marks of a LOT of little ponies. Hundreds, maybe thousands. It just gets to be a routine, you know?" She noticed everycreature in the room staring at her. "I guess you don't know. But don't worry, I can fix it!" She got out of her chair. "So where is the little brat?"
"Canterlot, locked up in the castle dungeons."
Starlight said, "That isn't even a hundred miles away. I still have a special connection with her cutie mark, you know, after what I did to her. I think I can fix it from here."
***
In the lowest, darkest level of Canterlot Castle's dungeon, two Royal Guards led Twilight, Spike, and Starlight down a hallway. Somewhere, water dripped, making sounds that must have been annoying to listen to if you were locked up here for more than a few minutes.
One of the guards said, "I thought her cell was right here. But I can't find it." He turned to the other guard. "What do you think, Brave Pinion?"
The other guard shrugged. "I woulda thought her cell was here...but it ain't. So I got no opinion."
A faint, childish voice said. "Are you here to bring me more blocks? I'm all out!"
"She's out!" the first guard shouted. "Alert the castle! Cozy Glow has escaped!"
The childish voice said, "I'm not escaping! That would be bad, right? But I'm all out of blocks to build with. I've already taken apart half of this level and put it back together different, but I'm running out of building blocks!"
Twilight said, "Cozy? Is that you?"
"It's me. But I've trapped myself in here. Can you come get me?"
In a flash of magenta light, Twilight disappeared. A moment later, she reappeared with Cozy Glow beside her.
Starlight bent down to inspect the filly's cutie mark. "Yup," she said. "Her mark's fixed. Now she's just a regular construction worker."
Cozy Glow smiled up at Starlight. "Hay, babe! Anypony told you today what a hot mare you are? I'd LOVE to show you a good time."
Twilight sighed. "Well, our expert says Cozy is all better now. And she passes--"
"Hay, pretty princess! I can make you feel like a QUEEN." Cozy waggled her eyebrows. "Want to find out more? I can--"
Twilight interrupted, "Shut up, Cozy." She said to everypony, "I think Cozy qualifies for work release. And I know the perfect place to do it."
***
Six months later, a bugbear rampaged through Ponyville, demolishing buildings left and right.
Darting through the air to dodge the monster's claws and teeth, Rainbow Dash complained. "Bugbears AGAIN? I'm so glad I live in a cloud house in the sky. Because if I lived on the ground here, I don't think my house would last three weeks. So much rebuilding, all the time."
Cozy threw a shovel at the monster. The tool hit the bugbear's nose dead center, making it howl and put its giant paws over its face. "I know!" Cozy squealed. "Isn't it WONDERFUL?"
Author's Note
Thanks to Sockpuppet for feedback on some key points.
"...like a villain looking forward to teaching an innocent, naive student to transform all the villain's enemies into teacups and smash them into pieces."
I suspect this line is partly inspired by SparklingTwilight's story "Unforgivable?" (And also, to be fair, by MLP episode canon.)
(Does this imply Maud Pie's pet, Boulder, might be one of Starlight Glimmer's nemeses? 
)
Woud you like to know one of the things I wonder about? Whether I should have tagged this story as a "Mystery?"
