Daring Do stepped out onto the swaying dock, feeling it sway crookedly beneath her hooves. She waved her thanks to the captain of the little boat, then turned and trotted down towards the small collection of flickering lights, hoping that the sea village would have a free room somewhere. It wasn't that she got seasick, but it was rather easy to feel tired when a pony had nothing to do but study a hoofful of old papers for hours at a time.

She remembered wryly how her friend, Professor Tabula Rasa, had stressed just how important this expedition was. The treasure was supposed to have some mysterious power, and the last thing anypony needed was for Ahuizotl to get his hands on it. When she had asked why this needed more importance attached to it than other missions, the good professor had swelled up and stated some of the most striking words she had ever heard: "Are you even pretending to listen to me, Rainbow Dash?"

The blue pegasus blinked. That didn't seem right, somehow. "Huh?"

There was a short sigh, and the pegasus' attention was drawn upwards to the exasperated purple unicorn standing before her. "Rainbow, everything's all ready with the machine. It's been all ready for the past five minutes."

"Yeah, yeah, that's great," Rainbow Dash said, waving an idle hoof. "Give me a moment, will ya? It's just getting into the action here. Well, more like the setup I guess, but it's an action setup."

"Rainbow, please! Rarity's going to be here any moment now, and she'll be very disappointed if she can't get a Downspiral Diamond quickly enough for her to complete her headpiece in time!"

Rainbow Dash raised an eyebrow. "Uh, hello? Fastest pegasus in Ponyville here? I can get hooked up to that thing before you know it. Chill out, Twilight."

Twilight Sparkle glanced over her shoulder at the rickety-looking machine looming behind her. The strange contraption's gnarled bent-over shape made it resemble an aging tree, yet it was tall enough and broad enough to blot out most of the view of the library's interior. "Do you know where you're supposed to go?"

"Where I'm supposed to go?" Rainbow repeated. Her eyes darted over its various components; aside from the rollercoaster-like track darting through the large holes in its structure, she had to admit that none of it looked even the faintest bit familiar to her. She yawned and tapped her chin almost thoughtfully, deciding that it was too weird to make any sense. "Nope, can't say that I do."

Twilight's horn flared up with violet magic. "Well then, I guess I'd better show you."

"What? Oh, come on!" Rainbow squirmed as a similarly-colored glow lifted her up into the air, depositing her onto the track's highest point before dissipating. "I could've totally flown up here by myself!"

"Well, I'm sure you could have if you weren't so into your book," the unicorn replied wryly. With a bit more concentration, she readjusted her friend's hooves so that she could strap them securely onto the miniature wheeled platform attached to the track.

"Hey, that wasn't just any book! That was Daring Do and the Cove of Candles! Seriously Twilight, I'm already on book eight!" Settling down onto her stomach, Rainbow looked down wistfully at the desired book, which was still tantalizingly opened to the page she had left it at. "I'm only a couple pages into it, and it's still way more interesting than this gigantic doohickey."

"It's not a doohickey—" Twilight began, only to be interrupted by a sudden knock at the door. "Huh? Oh, yes, come in!" she called, trotting about hastily as she made another last-minute check-over on the random assortment of levers and blinking lights. "That's probably Rarity."

Rainbow cast her eyes up towards the top of the machine, which unhelpfully blocked her view of the ceiling with its intermittent puffs of steam. "Gee, really?"

Seconds later, a white unicorn stepped inside, her elegant violet mane and smooth velvet saddlebags bouncing slightly with each hooffall into the library. She soon skidded to a halt, however, and her eyes widened at the sight of the mechanical monstrosity. Rainbow couldn't help but snicker at her astounded expression.

"My goodness," the newcomer said once she had found her voice. She poked at its unmoving side with a tentative hoof, while looking up at it warily as if fearing it might suddenly collapse. "This is … did you really build this in two hours, Twilight?"

"I sure did!" Twilight exclaimed, beaming proudly. "It would have been an hour and a half, but then somedragon thought it would be a good idea to go on an ice cream splurge. Again."

A pained groan floated from the direction of the kitchen.

"Oh dear," Rarity said, stifling a sympathetic giggle. "I do hope poor Spike is all right. He's done a marvelous job with the metalwork over here."

"Hey, I helped too!" Rainbow remarked, trying to dart down and grab some recognition for herself. She failed to do so, however, since the machine hadn't been set in motion yet. "I put all these holes in it, and that's definitely the most important part!"

"Yes, I can see that," Rarity agreed, and Rainbow scowled at the hint of amusement in her voice. "Oh, this is just marvelous, Twilight! Positively stunning! But you really didn't have to go to such lengths to set this up for me. When I said I needed a Downspiral Diamond, I was thinking more along the lines of heading down to Tartarus and finding one on my own. I didn't mean to trouble anypony to go to the lengths of creating … this."

"I know, but I took the liberty of doing some research of my own on them," Twilight replied, levitating a pair of goggles and stretching them over a somewhat irritated Rainbow's eyes. "It turns out they can't survive long in the sunlight without being properly cut and processed, and they can't be cut or processed without being cured in distilled ectoplasm first, and since ectoplasm would draw all the monsters toward you, it would be way too dangerous in general."

"Yeah," Rainbow added with a smirk, "and you wouldn't last very long down there anyway! I mean, how long do you think you could trek through all that mud and ash or whatever without fainting?"

"What Rainbow means to say," Twilight cut in with an exasperated glare, "is that we understand how important it is that you get the Diamond as soon as possible. Besides, what are friends for? You've gone out of your way for us more times than even I can remember, so it's the least we can do to return the favor, right?"

"I …" Rarity seemed to be at a loss for words. Putting a hoof to her chest somewhat dramatically, she smiled at Twilight. "I … Well, thank you. Both of you." She turned her gaze up towards Rainbow, who was astonished to see a hint of wetness in her eyes. Then the moment was gone as she seemed to recollect herself, and she called out towards the kitchen, "Thanks to all three of you!"

"Mmmuh … no problem, Rarity," Spike called weakly back.

"Well, I suppose that since you insist on doing this, I might as well avoid Tartarus," Rarity went on with a light laugh. "Is there anything I can do to help?"

"I don't think so." Twilight was staring up at her creation with a rather unnecessary level of fondness. "All we need to do is flip the master switch. Rainbow Dash will provide the necessary energy, and then I can take it from there."

"You're welcome," Rainbow said to nobody in particular.

"Very well."

There was a long moment of silence. A fly buzzed somewhere unseen, and Twilight awkwardly began to telekinetically draw the curtains, cutting off the dusty rays of sunlight one by one.

"… Twilight," Rarity finally said hesitantly, "is this, er, project … is it safe?"

"Most likely," was Twilight's response. "From my research it doesn't look as though this has actually been done before, but I've done the calculations and there's only a four-point-three percent chance of spontaneous combustion—"

"Wait, this hasn't been done before? Ever?" Rainbow's eyes darted from one section of the suddenly terrifying machine to the next, not quite able to hide her sudden surge of panic.

"Technically this has never been before successfully," Twilight corrected herself. Once the room was perfectly dark, she turned to the control panel nestled comfortably at the machine's base. "But there's really no need to worry about it, Rainbow. I've done extensive study into past attempts, and it seems that their main flaw was their insistence on adding three drops of nitroglycerin to the reaction chamber mix instead of two. If we can avoid tearing too many gaping holes through other dimensions, this should work perfectly."

Rainbow bit her lip. "Tearing holes …?"

"Twilight, dear, this might not be such a good—"

"Oh, it'll be perfectly fine. Would I really put any of my good friends through something dangerous?"

Rarity and Rainbow exchanged a look at that.

"Okay, let's do this." Twilight pressed a few buttons excitedly. A low whine emanated from the depths of the contraption, and she hastily pulled on a pair of nearby goggles for herself. A few lights began to flash from random sections, eliciting a satisfied nod from the purple unicorn. "Get ready to fly, Rainbow Dash! Oh, and Rarity, you might want to find some cover."

"Why would I—"

Twilight flipped the master switch.

The whining noise abruptly turned very shrill, echoing off of the library walls and causing everypony to cringe. The wheeled platform began to move, rolling down the steep track with quickly increasing speed, and with gritted teeth Rainbow Dash unfolded her wings and began to flap them as if she were actually flying rather than strapped tightly down.

As she took a nosedive through a wide hole and into the depths of the machine, she was surrounded by total darkness — she felt herself abruptly pull out of the drop, swinging around into a tight loop with a gradual upward incline. She pulled more deeply with each wing-beat, fighting the tug of gravity as she spiraled up and up and up, and each loop grew wider and wider until she suddenly shot out through another hole, emerging near the top of the machine. For a couple of seconds she took in the blurred sight of Rarity and Twilight watching intently from a makeshift shelter behind a bookcase, with Twilight's goggles reflecting the machine's glow; then she plummeted into the blackness again, and they were gone.

Heh, that wasn't so dangerous, she thought, narrowing her eyes in pride. Fifteen seconds for one lap? I can do better than that. Let's see how fast this thing can go …

Spinning in another tight spiral, the blue pegasus lowered her head down to the platform, letting the track lead her up and around again. The rustling of her wings echoed off the machine's interior, and she could feel a cool breeze being left in her wake. The machine's whining, she realized, couldn't be heard in there at all. Weird.

Flying out from the top again, she found herself grinning at the dizzying rush. "Faster?" she called out.

"Faster!" Twilight agreed gleefully, and then she was lost to Rainbow again.

On the third lap she noticed a bit of light within the machine for the first time: a bluish spark dancing in place in midair, right at the center of the spiraling track. Normally it would have been unimpressively dim, but in that darkness it cast strange shadows that shifted and swayed as Rainbow darted around again. Its glow grew a bit stronger on the fourth lap though, and on the fifth lap it was nearly as bright as the library's lighting, forming a pale streak that danced before her eyes every time she looped around it.

"Ectoplasm!" Twilight announced as Rainbow began the sixth loop.

"Wait, what—?"

What she saw upon plunging in again nearly made her wings lock up in surprise: a vent had opened up beneath the spark, and a thick jet of greenish steam was beginning to shoot out of it. Her mouth hung open for a few seconds, catching the air and making her cheeks billow out; but then she quickly snapped it shut, hoping that it wasn't going to plug up her airway or something.

"Rainbow!" Twilight said when she next emerged.

The pegasus gasped for air. "What?"

But Twilight's words were swallowed up the hissing steam as Rainbow dove into its depths again. The spark was now a long brilliant sliver of light, and it seemed to be greedily soaking up the distilled ectoplasm. It looked rather distorted through her goggles, but the sight wasn't quite so important right now.

When she shot out again and used the opportunity to catch her breath, she heard Twilight shout her name again. "What?" was her irritable response, but again she missed the reply.

Oh, I'm so gonna lay it on somepony for this.

By now the light was practically blinding, and she had to squint in order to see the rainbow trail that was now being left in her wake. She allowed herself a little smirk, but it quickly melted into a look of shock as a contingent of knives supported by mechanical arms burst into view, weaving in and out to cut easily into the shiny thing emerging from within the light. She yelped as one was pulled out of her way just in front of her, missing her muzzle by inches.

The outside flashed by again in a blur, and she used the opportunity to roar, "Twilight Sparkle—!"

"Rainbow, don't—!"

By now she was going so fast that shapes were swimming in her vision, distorted and unrecognizable even from anything in her dreams. The light was like a miniature sun blazing with the colors of her own rainbow, glinting cruelly off of the dancing blades, and she was forced to squeeze her eyes shut; but the shapes still twisted around against the backdrop against her eyelids. The now-shrieking steam drowned out the familiar whistling of wind in her ears.

Dizziness gripped her; gravity pulled on her from all directions at once; the shapes darted around her and through her. Trying to shake herself, she urged her wings to flap faster, faster. She had to end this. She had to end this.

"Don't hold your breath!"

Her body seemed to have been waiting for that senseless command; she gulped for air as she pulled out of the dive yet again, in spite of the ectoplasm still jetting up within the spiraling track.

It was then that a dazzling chromatic flash, brighter than anything yet, exploded outwards with a force strong enough to push the speeding pegasus right off the track, smashing her through the machine's wall and into the library's. Feeling as if she were still spinning around, she heard herself groan as she slid down to the floor, crumpling up in an exhaustive heap.

The machine's whine was beginning to die down, allowing panicked voices to reach her ringing eardrums:

"—bow Dash, are you all right—"

"—no, no, this wasn't supposed to happen—"

"—fire extinguisher right here, Twilight—"

"—I'm sorry, oh my gosh, I'm sorry—"

"Rainbow! Can you hear us, Rainbow, are you all right?"

She looked up dizzily into a trio of blurring Raritys, all leaning down toward her with horrified concern. They all reached out and touched her forehead with three white hooves, but she could only feel one. Weird. She must have hit something pretty hard.

"'m all right, Rarity," she assured her, grinning weakly. "Chill out, all three of ya. 'm fine. I dunno if your diamond thingy's okay though. You might wanna check that out, darling."

With that she spiraled into unconsciousness, barely registering the unicorn's shocked exclamation.