>It was a dark and silly night when P.I. Pie received her latest case. There were no ponies on the streets and no crumbs in her sheets as she sat staring at the hastily scribbled note that had been wedged into her window. 
>“Meet me where the bubble gum sounds twice,” it read. 
>The writing was familiar. Lyra Heartstrings was Pinkie’s most active informant, often getting herself into trouble for what others might consider useless news, but they both knew better. Things were never as they seemed, not in Ponyville. 
>“Well, Gummy,” she said, fishing out her detective outfit from the closet, “I’ve got some business tonight. Don’t wait for me, I’ll be back late.” 
>Gummy blinked.
>Pinkie sighed. “You know I have to go. There are ponies depending on me.” 
>Another blink.
>“I promise,” she smiled, kissing her pet alligator’s head on the way out the door. “Besides, Lyra’s never led me wrong before. Everything will be fine.” 
>The train station was quiet as Pinkie approached, as expected at such a late hour. Her informant was nowhere to be seen, but the twitching in her left ear told her she wouldn’t be waiting long. 
>Right on cue, the mint green unicorn stepped out of the shadows, her face hidden by a mask fashioned to look like her own face, complete with a paper mache horn covering her real one. Pinkie had to admit it was a brilliant disguise. 
>“Were you followed?” Lyra said under her breath. 
>“Were you?”
>Both mares turned to look over their respective shoulders, finding the streets just as barren as before. They sighed dejectedly at yet another night without a chance to use the coded language they had worked so hard on. They could use it anyway, but it just wouldn’t be the same. 
>“So what’s the dilly, good filly?” Pinkie asked, pouring bubble fluid into her pipe. 
>Lyra mumbled something, looking off to the side. 
>“…Sorry, could you repeat that?”
>“Sweetener,” she gritted out. “Twilight has been getting zero-calorie sweetener from Canterlot.”
>Pinkie felt a pit form in her stomach. Twilight? Her Twilight? There was no way that could be true.
>“How sure are-”
>Before she could finish speaking, Lyra tossed something onto the ground between them. It was a familiar packet of a substance no pony would willingly consume. A substance you couldn’t find anywhere in Ponyville. Opened. Empty. Pinkie felt sick. 
>“This was in her garbage.”
>“I… I think I need a minute.” Pinkie sat down, her bubble pipe lying forgotten next to her.
>“If it’s any consolation, you’re the only one I told. I don’t think anyone else knows.” 
>Sweetener. The word echoed in Pinkie’s mind. It was innocent enough on the surface; sugar was a sweetener after all. But ask any pony in Equestria and they’ll tell you that sweetener means “not sugar.” It’s a replacement. And to top off this nightmare sundae, Twilight was using a zero-calorie version. 
>“Twilight,” Pinkie thought to herself, “what happened to you?” 
>Lyra piped up again, pulling Pinkie from a storm of thoughts too dark to describe. 
>“Whatever you’re planning, I want in.”
>Pinkie hadn’t planned anything yet, but she kept that part to herself. 
>“Are you sure, Lyra? Things might get criminal.”
>The unicorn lifted her mask and raised an eyebrow, nudging the packet with a hoof. The meaning was clear. 
>Pinkie nodded solemnly as a plan finally started to take form in her head.
>“Do we know how often these shipments come in?” she asked.
>“No,” Lyra smirked, “but I can find out.” 

>The next morning, Pinkie sat anxiously on a bench in the park as she waited for Lyra’s return. It had been nearly six whole minutes since they separated, and there was no telling how badly things might be going. 
>At minute seven, just as she was ready to start a missing pony search, she spotted Lyra making her way to the bench. At first Pinkie was relieved, but the expression on the other mare’s face was tense and defeated. 
>“What happened?” she asked as soon as they were within earshot of one another. 
>“Nothing bad,” Lyra sighed. “Just had to be a little more direct than I’m used to.” 
>That didn’t sound good.
>“How direct?”
>“…I had to ask Spike.” 
>Pinkie winced sympathetically. She had nothing against Spike, but it was way more fun to find things out on your own without needing to ask. The fact that Lyra lasted so long before giving up was a testament to her experience. 
>“What’d you find out?”
>“Shipment came in less than a week ago. They ordered a box of two hundred packets.” 
>“Darn,” Pinkie stomped. “She’s set for a while, then. Cutting off her supply is no good.”
>“Plan B?” Lyra suggested.
>“Plan B.”
>It would be far more dangerous than simple mail fraud, but it would arguably be more effective. They had wanted to save it as the backup plan because neither one was looking forward to hurting Twilight. However, it seemed like that could no longer be avoided. 
>Both mares nodded grimly and began walking to the library. Along the way, Pinkie grabbed her stash of rope and… other items. She saw Lyra shiver in the corner of her eye, but the silence held. 
>As they approached the door of the giant tree, Lyra put on her Lyra mask. Pinkie had no such comfort. 
>*knock knock knock*
>The door opened, revealing Twilight’s bemused smile. Before she could speak, a stream of water hit her in the face. Her expression went from shock to one of mild annoyance as she saw the water gun in Pinkie’s hooves. 
>“Pinkie, really? What was that for? And why is Lyra-“
>Another stream of water cut her off. Pinkie felt the tears welling up in her own eyes. She didn’t want to do this. 
>“Stop that!” Twilight stamped a hoof, lifting the water gun into the air with her magic. 
>While she was distracted, Lyra started to wind the coil of rope around Twilight’s body. Pinkie let her tears fall freely as she pulled another water gun from her mane. 
>“Why don’t you like sugar, Twilight?” she whimpered, taking aim once more.
>“…I’m sorry, what?”
>Twilight didn’t even fight back as Lyra finished wrapping the rope around her barrel. It wasn’t enough to restrict her movement or anything, but boy did it look uncomfortable. 
>“You’re using sweetener,” Pinkie said through her tears. “Zero-calorie sweetener.” 
>“I found this while digging through your garbage!” Lyra pulled out the empty packet and threw it at Twilight’s hooves. 
>Twilight was so confused. 
>“Okay, first of all: that’s weird, Lyra. Second-”
>Yet another stream of water. Twilight was once again unamused. She spit out the bit that had gotten in her mouth and continued. 
>“Second: what does that have to do with,” she waved a hoof around, “all of this?”
>“Don’t play silly with us!” Pinkie cried. “Spike told us everything!” 
>“I did?” 
>All three ponies looked behind Twilight at the confused expression of Spike as he stood there in an apron. He waved. 
>“Hey, Pinkie. Hey again, Lyra.”
>Lyra waved back, a bright smile showing through the mask's eyes. 
>Pinkie sprayed him in the chest. 
>“Aw man,” he sighed, his apron now soaking wet. 
>Twilight rolled her eyes and took the second water gun from Pinkie’s hooves, as well as the mask from Lyra. 
>“If Spike told you, then why are you even upset?” Twilight asked. “I didn’t think either of you cared that much about bacteria.”
>Pinkie and Lyra blinked at each other, sharing a look of utter bewilderment. Twilight slowly facehooved. 
>“You have no idea what I’m doing, do you?”
>“You hate sugar and you’re using a sweetener to replace it,” Pinkie stated. 
>“No? And even if I was, that doesn’t justify spraying me in the face and… I guess wrapping a rope around me?” She lifted the rope away, stepping out of the ineffectual loops. 
>“Darn, she’s good,” Lyra muttered. 
>“I told you, she’s super smart,” Pinkie whispered back. 
>“Since neither of you care enough to ask, I’m using the sweetener as food for several colonies of bacteria I’m studying from my gut. It would grow faster with straight sugar, and I don’t want that.” 
>Pinkie took a moment to register the odd collection of words.
>“So you still use sugar in your foodstuffs?”
>“Yes, Pinkie,” Twilight deadpanned. “When a recipe calls for sugar, I use it.”
>“And you’re using the sweetener to grow a bio-weapon.” 
>“What? No!”
>“Well now I’m even more confused!” Pinkie threw her hooves in the air. “What the booty butt do you need bacteria for?”
>“To study! There’s a lot we can learn about how our digestive system works by studying the bacteria that live inside us.”
>“Sounds like propaganda, but okay,” Lyra shrugged. “As long as you’re not turning into one of those weirdos that thinks sweetener actually tastes better than sugar.”
>“No, I’m not, but even if I was, that still wouldn’t justify-”
>Pinkie sprayed her in the face with a third water gun. 
>“Run, Lyra!” she yelled.
>Both mares split off, leaving a lightly fuming Twilight and a sad Spike in their wake. 
>Another successful case for P.I. Pie.