Chapter One: Mirror, Mirror  “Okay, explain it to me again.” 
  Twilight Sparkle laughed as she gestured upwards with a hoof, her wings drawn tight against her sides. “Tonight’s lunar phase is called a ‘waxing crescent’. Sometime next week, it’ll be a half-moon, and then it’ll phase into a ‘waxing gibbous’, and then a full moon.” She smiled and noted, “One down, twenty-nine to go.” 
  It was a crisp spring evening in Canterlot proper, the moon hanging overhead in the night’s sky and only the odd cloud dotting the nightscape. Twilight smiled, knowing full well that Princess Luna was no doubt proud of the work she’d put into the evening sky and glad that she could enjoy them. They’d been nice prior to her return, of course, but now that she was back, they’d been spectacular. 
  “I still don’t get it.” While the beauty of the night wasn’t lost on her companion, Spike was nonetheless focused on other things, clipboard and quill in hand as he scribbled down notes. “I mean, I get that we’re one moon closer to Sunset coming back, that I understood perfectly. It’s this lunar phase thing. I kinda get why they’d call it a ‘crescent’, but ‘waxing’? And what the hay does ‘gibbous’ mean anyway?”
  The alicorn shook her head as the two continued on their way through the castle gardens at Canterlot, back in town for a brief stopover following Twilight’s goodwill tour of Equestria before their return to Ponyville in the morning. It would be good to get home and get back to running her library, but for now, she had to deal with a stubborn learner. “Alright, one more time. It’s called ‘gibbous’ because…”
  “Twilight Sparkle.” Her attention snapped in front of her to a grey earth pony, dressed in a nondescript jacket and fedora hat, his dark grey eyes fixed upon her and Spike. “There is more than one of everything.” 
  “Huh?” Mare and dragon looked to one another for a brief second before turning back to the stallion, Spike asking, “What do you mean…? Whoa!” The stallion had vanished, with seemingly no trace left behind to even mark his presence, and the dragon felt a chill as he noted, “Okay, that was weird.” 
-
  “What do you think, Tibbles? Is this not a glorious evening?” Princess Luna turned her gaze upon her animal companion, who responded with an enthusiastic nod and a thumbs-up. She laughed and turned back to the night sky, basking in her work from one of the many high windows of Canterlot Castle. “Agreed. The moon is a lovely waxing crescent…” She brought a hoof to her chin and wondered aloud, “I still wonder how that terminology came about.” She dismissed the thought and continued, “Regardless, ‘tis a beautiful evening to observe the moon, and any evening is a good one to not be banished to it.” She sighed, glad that ordeal was long over, and collected her pet before continuing on her way, Tiberius riding upon her back. “Now then, to the official transition to the night shift and…” 
  She paused as she looked into the throne room, catching sight of her sister as her magic went to work upon a large artifact, one that looked strangely familiar in light of recent events in the Crystal Empire. “Sister?” She slowly approached, Celestia seemingly not having heard her as the artifact, now clearly some sort of mirror with a horseshoe design, took on a bright blue glow. As Luna watched in surprise, Celestia dashed into the mirror, vanishing from sight with a flash. “Celie!” Luna dashed forward as the glow faded from the mirror, gently prodding it with a hoof before lifting it over her head with her magic and letting loose with the Royal Canterlot Voice, “SISTER! GET THINE HINDQUARTERS BACK HERE THIS INSTANT!” Horror sunk in, and she gently lowered the mirror as hurried hoofsteps approached. “Oh dear.” 
  “Princess Luna!” Accompanied by a pair of ponies from the Night Guard came a familiar unicorn stallion, pince-nez perched on his snout as he asked, “Whatever has happened?! Where is Princess Celestia?!”
  Luna took a breath to calm herself before addressing her subordinates. “I do not know for certain, but I will not stand idle. Kibitz, all scheduled events for the evening are to be postponed or cancelled by my authority until further notice. Guards?” The two guardsponies stood at attention as she ordered, “Princess Twilight is still in Canterlot; I ask that she and Spike be brought to me immediately, and that the other bearers of the Elements of Harmony be summoned forth-with from Ponyville. Dispatch my personal chariot, and see to it that the Elements themselves are fetched from the Golden Oak Library.” 
  The guards snapped off quick salutes and rushed to fulfill their orders, Kibitz remaining and giving his diarch an uneasy expression. “Highness, while I appreciate your concern and quick action, I must ask, why the Elements of Harmony? What good…?”
  “Past experience has encouraged me to take precautions, Kibitz.” Luna turned her attention back to the mirror and explained, “I know very little of what’s going on, but what little I’ve seen discourages my optimism. And calling forth Princess Twilight and her friends appears to be the standard procedure of late; why not make certain they are properly equipped?” 
  “Very well, but I still do not understand. Where is Princess Celestia?” 
  The Princess of the Night kept her gaze upon the mirror as her pet caught up with her, long having been thrown off her back in her haste. “Beyond our reach.” 
-
  “Forgive me for my complaint, Princess Luna, but could this not have waited until the morning?” Rarity pawed at her styled mane as she examined herself in a small mirror. “A proper lady needs her beauty sleep…” She paused and turned sharply, all but screeching, “PINKIE PIE! LEAVE THAT BE! YOU’VE NO IDEA WHERE IT CAME FROM!”
  Applejack, slightly less concerned for her looks but equally miffed as Rarity at having been summoned in the dead of night, glared at her fellow earth pony and newfound kin, who sheepishly stopped prodding at whatever she’d been examining under the table. “Seriously, Pinkie, we got us a crisis here.” 
  “I know, but I focus better when I’m chewing on something, and that gum…”
  “Is disgustin’.” 
  Pinkie pouted, the rest of the gathered ponies (and dragon) having varied looks as they turned to business at hoof, Fluttershy summarizing, “So, Princess Celestia vanished through a magic mirror earlier tonight?” 
  “Indeed.” Luna gestured with one wing towards the mirror in question. It was less ornate than the Crystal Mirror or its counterpart, the so-called ‘bridge mirror’, without the decorative bit on the top with a stylized pony or bridge illustration, and its coloring and gems were different, but they were clearly of the same line of development. “I attempted to follow, but it was solid to the touch after my sister passed through it. I suspect that it operates differently from the other mirrors.” 
  “You suspect?” Twilight regarded her fellow princess anxiously and asked, “Luna, we all know that Star Swirl the Bearded created the Crystal Mirror and the bridge mirrors. Assuming he made this one too, why would it work differently? You were there when he made them, weren’t you?”
  Luna sadly shook her head. “Alas, no. While I considered Star Swirl a friend, I was not as close to him as my sister was, and not privy to his study of parallel worlds. By the time his efforts began in earnest…” She lowered her head in shame and admitted, “I was taking those first few steps down the slippery slope that led to Nightmare Moon. T’was not a happy time for me.” 
  Her vanity forgotten in her sympathy, Rarity quietly approached. “Princess, you need not elaborate.” The two shared a smile before the fashionista prodded, “But if you know nothing of this mirror or how to open a portal with it, then how can we be of help?”
  “I know nothing for certain, but I’ve my suspicions. Please, follow.” She led them out of the quiet meeting room and along a well-lit hallway, continuing her elaboration on the way. “Shortly after I found out about the Crystal Mirror and its ilk, I combed what I could of the castle libraries for information upon it and its development. Alas, I found little beyond what Sunset Shimmer no doubt did prior to her departure from our world, and nothing about how it was made.” 
  “But some record has to exist somewhere!” Twilight quickened her pace to walk beside Luna as she explained, “The Crystal Mirror is a unique magical achievement! You don’t just forget how you made a portal to another world!”
  “Indeed, no, but I suspect Star Swirl opted to hide the information away somewhere secure. Most likely, one of his original libraries.”
  “Hold on there, Princess!” Applejack closed in and noted, “Ah ain’t questionin’ yer logic, but if’n Star Swirl had a library somewhere in the castle, wouldn’t Twilight know ‘bout it?”
  “Maybe it got turned into a craft room or a home gym?” Pinkie ventured. “Not like you couldn’t use one around here.” 
  Twilight shook her head. “No, I’ve memorized every renovation this castle’s had since it was built. None of the libraries were turned into anything else, on Celestia’s orders.”
  “And his personal libraries were not in the castle proper, but deep within the mountain upon which Canterlot was built, protected by a complex cave system and no doubt other security devices. Star Swirl did not believe in allowing any random plebian access to his works.”
  “So, do you know where it is?”
  “Alas, no.” Luna frowned and admitted, “Apparently, I am one of the plebians.” 
  “Oooh, me too!” Pinkie perked up and declared, “Rarity calls me a plebian all the time, whatever that means!”
  “I assure you dear, it’s purely meant as a term of endearment.” Her nervous smile faded, and Rarity quietly noted, “One of these little adventures of ours, I’d like to go somewhere pleasant. A tropical island paradise perhaps, rather than the innards of a mountain.” 
  “Yeah, just remember the last time we went to the tropics.” Rainbow Dash grinned as she recalled their adventures beneath and upon the high seas, but quickly got back to their current adventure as she countered, “Seriously Rarity, where’s your sense of fun?”
  The unicorn held her head up high as she answered, “In the comfort of Aloe and Lotus with a hooficure, thank you very much.”  
  Luna opened a massive wooden door before them, leading into a cavernous room containing various artifacts of bygone times, crates and barrels surrounding them as they approached an impressively-sized set of doors. “In any case, if anypony can navigate these caverns, it is you, Twilight. My sister speaks often of your intellect; rare is the time where she doesn’t compare you favorably to Star Swirl himself. Perhaps you can channel that parallel on this quest.”  
  Twilight looked aghast as she turned to Luna once more. “She really compares me to Star Swirl?”
  “Yes.” Luna grinned and noted, “Personally, however, I see more similarities betwixt you and my sister in her youth than I do you and Star Swirl.” She gestured to Pinkie Pie as the party pony inspected one of the barrels and added, “Star Swirl always came across more like her.” She allowed herself a quick laugh, then turned back to business. “Whatever you think you require for this excursion, I suggest that you gather it quickly. I would join you, but I must see to my royal duties before Kibitz has an aneurysm.”
  “Of course, Princess, we understand.” Twilight turned to her loyal assistant and called, “Spike, my note-taking supplies!”
  “Got ‘em right here!” The dragon lifted up her saddlebags, which she quickly took up in her magic and levitated onto her back. “Quills, ink, and lots of notebooks!”
  “What do you need all that for?” Rainbow Dash approached and asked, “I mean, can’t we just track down a book or something and bring it back?”
  “And risk damaging or destroying a magical relic? Assuming preservation spells are in place, Star Swirl’s journals and writings are at least a thousand years old! It’s better to copy what we find rather than disturb it.” Her supplies at the ready, Twilight turned to Spike and quietly added, “Spike, I think it’d be a good idea if you sat this one out.” 
  The little dragon looked up at her in surprise. “Really? But what if–?”
  “Celestia might try to send a message back using your fire mail, and Luna would want to be the first to receive word or send word back in return.”
  “A worthy point, and besides, I’ve already called for refreshments to begin my evening duties with.” Luna leaned down and prompted, “Would you truly like to miss out on hot cocoa?”
  Spike perked up and asked, “With marshmallows?”
  “Of course!” Spike gleefully hopped up onto Luna’s back as the princess called, “Best of luck to thee, my friends!”
  “Bring me back something awesome!”
  “We won’t let you down, either of you!” Twilight waved them off as she opened the doors, an ominous creak reverberating through the air around them. “Come on girls, we have us a library to find!”
  “A library deep inside a mountain, protected by who knows what?” Dash gleefully spun about in the air and cackled, “This is so Daring Do! Think we’ll run into a monster?”
  “Rainbow Dash, don’t you dare say somethin’ like that!” Applejack groaned and rolled her eyes. “That’s just invitin’ trouble!” 
  One by one, the six mares entered the chamber, Fluttershy lagging behind with a slight quiver to her hoofsteps. Once she entered, however, the chamber seemed to light up, lanterns high above their heads brightening and providing illumination. As she took in what she saw, she closed in with the rest and realized, “Well, this isn’t so bad.” 
  All around them were more artifacts of a bygone era, surprisingly well-preserved even considering where they’d been stored. Twilight’s eyes darted among the bits of furniture to the portraits to the assorted artifacts, all of them no doubt having a history to them simply by virtue of being possessed by Star Swirl himself. Being in his personal chambers, on a quest from a princess? Had Celestia not gone missing, this would be the best night ever!
  “Twilight?” She paused as Applejack came up beside her. “Sorry darlin’, but yer startin’ to fade out on us, and we kinda need ya to get around here.”
  A sheepish grin crossed the alicorn’s face. “Sorry, got caught up in the moment.” Her gaze found a directory, and she examined it. “Huh. I’m surprised Luna had so much trouble down here. Everything’s so well-labeled. It’s almost like I did it.” 
  “Well, if she’s anything like me, she probably gets bored and phases out once she sees enough big words.” Rainbow flew up and examined one of the signs high above them and explained, “See what I mean? Big words! I mean, I know what a cellar is, but what the hay is a ‘lucre’?”
  “That’s a fancy word for ‘money’, sugarcube.” 
  “Okay, what about a ‘larder’?”
  “Food stores, darling.” 
  “‘Besom repository’?”
  “Ooh! That’s a broom closet!”
  “Augh!” The pegasus’ eyes went to the weirdest word in the directory and asked, “Okay, so what’s an ‘athenaeum’?”
  “That’s what we’re looking for! The library!”
  “Then why didn’t he just label it ‘library’?!” Rainbow came down for a landing and stomped a hoof on the stone floor. “Seriously, I get this Star Swirl guy’s an important egghead and everything, but did he have to rub it in everypony’s face?”
  “Star Swirl wasn’t that bad, and besides, think of the history!” Enamored with her surroundings as she led them on, Twilight recounted, “He used to walk these very halls! We’re stepping in the same dirt that he stepped on!”
  Rarity gave the floor a distainful look and shuddered. “Couldn’t he have put in some proper flooring? Hard wood at least? Maybe marble?”
  “A thousand years ago was a very different time, Rarity.” Twilight closed her eyes, imaging it in her head as she led them on. “I can almost see it now.”
  -A Thousand Years or So Previous-
  “It’s an exciting day to be magical, Celestia!” Star Swirl had a look of manic glee in his eyes as he led his diarch and old friend through his chambers, the bells on his hat jingling with every hoofstep. “I’ve made a breakthrough that even I didn’t think possible, and that’s saying something! This mirror will be the greatest achievement of my career!” 
  Celestia was used to such pronouncements, but he had a tendency towards not exaggerating his claims too much. “Star Swirl, forgive me sounding incredulous, but a portal to another world? It just seems impossible.”
  “Oh, I assure you, it’s quite possible.” A dreamy look on his face, the old unicorn mage lifted a hoof for emphasis as he continued, “In time we may even be able to jump from one dimension to another! Can you imagine the possibilities, Celestia?”
  “Yes, but…” The princess turned thoughtful as she looked to the ground. “I doubt I can be of much help. Luna’s become so distant of late, and with my court moving from our castle to Canterlot, I’ve only had more to do.”
  “Ah, that.” With a dismissive wave of one hoof, he noted, “I know you’ve been concerned since your sister started to act a bit darker than normal, but I’m sure we’ll get her turned around before anything serious happens.” 
  A smile formed on the royal’s face. “Thank you, Star Swirl. I’ve needed some reassurance, given all the doubts I’ve felt lately.”
  “Never doubt yourself.” Pride was clear in his eyes as he recounted, “I knew from the moment I met you that you would do great things for your subjects. I have never gotten reason to think otherwise.” A wicked grin formed on his face, and he offered, “If nothing else, the two of you can go and trounce a dragon together. Thumping those brutes never gets old.” 
  A smirk. “You know, there’s a reason they’ve kept their distance from Equestria lately.” 
  “Hmm. Perhaps they can learn.” He shook his head and got back to the subject at hoof. “Anyway, onto more pressing matters; if the secrets of cross-dimensional travel are to be kept down here, do you think I should put up some protections? Perhaps a trained supernatural beast?” 
  Celestia smiled and jokingly suggested, “Maybe a hydra?”
  The old wizard clapped his forehooves together. “Oooh! I like that idea!” He then stroked his beard thoughtfully and wondered aloud, “Now where can I find some hydra kibble?”
  -The Present Day-
  “Now y’see Dash! If’n we’d been here when that thing was alive, we’d be in a heap’a trouble!”
  “But Applejack, we’re not in trouble!” Pinkie knocked her hoof against the massive skull before them. “It’s pining for the fjords! See?”
  “Oh dear, the poor thing!” Fluttershy hovered up and examined the immense skeleton, its multiple heads suggesting that they were seeing a long-dead hydra. “When we get done with this, I’m going to give it a proper burial.”
  “Really? I’d leave it here; it adds to the rustic, spooky charm!” Pinkie darted over to a coffin and asked, “Can’t you see stuff like this show up in a Haymer Horror movie?”
  The yellow pegasus landed and trembled. “Yes, but I don’t like those movies to begin with.” She picked up her pace and asked, “Twilight, how soon until we get to the library?”
  “Not long…aha!” Twilight pointed a hoof ahead towards an impressive stone structure, carved into the very cave and guarded by sculptures of manticores that seemed to be made of the very dirt beneath their feet. With perhaps a little too much enthusiasm, she trotted forward and pulled on one of the door handles. The door opened with a shuddering creak, stale air rushing out after untold decades of confinement. “Careful, girls. No telling what we’ll find in here.”
  What they found was an impressive interior, the front foyer alone packed with artifacts and relics, a bookshelf waiting on one side packed with objects from long ago. In the distance, they could see even more, as well as huge shelves packed with books that hadn’t seen the light of day in centuries. Light shone from above as they entered, and as Twilight looked about, she squealed with joy and darted from one object to another. “Omigoshomigoshomigosh! Look at it all! An original tome of Star Swirl’s Studies of Heavenly Spheres! His original diagrams for the uses of practical magic!” A gasp worthy of Pinkie Pie catching sight of a particularly tasty treat, and she darted over to a coatrack bearing a decorated, starry cloak and… “IT’S HIS ORIGINAL HAT! COMPLETE WITH BELLS!” She turned back to her friends and declared, “Nopony knows how he got it! There are so many conflicting stories about it!”
  “Fascinatin’.” Unimpressed, Applejack gestured towards one corner and dryly mentioned another feature of Star Swirl’s athenaeum. “Hey look, cobwebs.” 
  Rarity shuddered, but her attention was swiftly drawn to an impressive, greyscale depiction of the missing Celestia. “Oh my word!” She approached with an awestruck look on her face. “Have a look at this, dears! I’ve never seen Celestia look so young!”
  “Really?” Rainbow flew up to get a closer look at the portrait and noted, “She looks pretty much the same to me.” 
  “It’s the eyes.” Twilight looked up at the portrait and explained, “Even when I was just starting as her student, I could tell that there was something weighing her down inside. In hindsight, it makes sense, given everything that’s happened since this was made. Over a thousand years of living would be enough to make anypony look aged and weary.” 
  “Twilight?” Fluttershy approached, concern clear on her face at the unease of her friend. “Is something the matter?”
  “A lot of things, I guess.” The young alicorn sighed and turned to her friends. “When all of you were little fillies, what did you want to do when you grew up?”
  “Why, go into fashion, darling! What else?”
  “Ah’d’a been happy workin’ on Sweet Apple Acres with mah family!”
  “Flying with the Wonderbolts!”
  “I didn’t really know what I wanted to do – I just wanted to have fun! And maybe eat a lot of cupcakes!” Pinkie drew Fluttershy in close and added, “And I bet you wanted to spend lots of time with animals, didn’t’cha?”
  A smile formed on the pegasus’ face as she explained, “Actually, for a while, I wanted to be a dentist.” 
  Everypony else gave her surprised looks as Applejack asked, “Don’t tell me, that old Hearth’s Warmin’ story ‘bout the misfit reindeer?”
  “No, I just really liked flossing.” 
  Twilight shrugged and continued, “Well, ever since I saw Celestia raise the sun one year at the Summer Sun Celebration, I knew I wanted to study magic. I never saw myself becoming a princess like her.” She gestured with a hoof towards a large statue of Star Swirl himself, situated next to Celestia’s portrait. “I always thought I’d end up like him. I’d learn about magic and use that knowledge for the benefit of all Equestria. He did that, and look at all he accomplished!” She turned back to the portrait and continued, “Now it’s looking more like I’ll be following in her hoofsteps instead.”
  “Is that such a bad thing, darling? You’re a princess, after all! It’s every little filly’s dream!”
  Rainbow Dash rolled her eyes at Rarity’s remark. “Not mine.”
  “Maybe the crown and the castle, sometimes the power, but not the responsibilities that go with it.” Twilight turned away from the portrait and explained, “Ever since she took on the crown, Celestia’s had the weight of an entire nation on her back! She’s done so much for the good of Equestria, had to face so many hardships, from losing the Crystal Empire to banishing Luna! Who in their right mind wants that kind of pressure?!”
  The other mares looked among one another, and Pinkie admitted, “Yeah, that does sound kinda scary.” 
  “Like lookin’ after the farm cranked up so far the dial done broke off.” Applejack gave a reassuring smile and noted, “But you’ve done some mighty impressive things yerself sugarcube, and you’ve got somethin’ Celestia didn’t have. Us.” 
  “And who says you can’t be a magic wonder of the world and a princess with awesome responsibilities?” The speedy blue pegasus noted, “And that sounded way more reassuring in my head.” 
  “Regardless dear, we’re all confident that you’ll do well.” 
  General murmurs of affirmation went out with Rarity’s reassurance, and Twilight smiled. “Thanks girls. Come on, let’s see if he has a directory.” She led them towards the bookshelves in the distance and noted, “Of course, this predates the Dewhoof Decimal System by several centuries, so here’s hoping there’s some similar labeling system in place.” 
  “Only less eggheady than the one that led us here.” Rainbow quickly spied a set of signs and flew over. “Hey, I think I found it! This says ‘Research on Mirrors’! If that’s not a good place to start, I’ll eat my mane!”
  Twilight gleefully retrieved several books and scrolls from the shelves with her magic and levitated them over to a nearby table. “Okay everypony, be gentle. Star Swirl’s put some strong preservation spells on these, but even those run out with time, and we can’t afford to lose a single page.” 
  “Got it, handle with care.” Rainbow carefully unfurled a scroll and examined it. “Whoa. We’re definitely on the right track.” The other mares gathered around her find to see an illustration of the Crystal Mirror and complex equations on its workings. “Why does this say ‘Mark vee-eye-eye-dash-ay’?”
  “Roamin numerals.” Twilight checked the dates and added, “This was drawn up shortly before Princess Luna became Nightmare Moon. The Crystal Mirror and the bridge mirrors may have been the last ones he made. But why did he stop? And how much earlier was the model that Celestia used?” She went back to her book and opened it carefully, her eyes widening as she exclaimed, “Girls, Star Swirl made an index book! Right here!”
  “Would somethin’ like that really be necessary?”
  “Of course! Any magical researcher or inventor worth anything knows the value of documentation and recording their work! And with this much recorded, having a quick index guide is crucial!” Her eyes scanned the index as she read, “Right here at the bottom, all of the journal entries for the creation and uses of the Mark Seven-A and Mark Seven-B mirror portals!” She went back up to the top, quickly checked over the numbers and figures, then pulled a few more books and a scroll from the shelves and gently opened them. “Here we are, everything on the mirror portal Celestia left through, his Mark One.”
  “The very first one?”
  “And the prototype for all the portals that came afterwards, and it’s all right here; every detail on how they work, every failure in making them…” Twilight’s eyes widened as she looked at one such entry and exclaimed, “And every world that he and Celestia visited?!”
  -
  “There it is! Every bit of magical knowledge all wrapped up in one reflective package!” Star Swirl beamed as he noted, “Should we ever find those inquisitive counterparts of yourself and Luna, I’ll have to thank them for the inspiration.” 
  Celestia eyed the mirror carefully, her mind already considering the implications of its aesthetics. “It looks like a jeweled upside-down horseshoe.” 
  The old wizard gave her a disbelieving look. “Don’t tell me you believe in such silly superstitions?”
  “No, but…never mind. How does it work?”
  “Ah, there’s the rub!” Star Swirl grew more animated as he explained, “Some worlds can be accessed through the right combination of spells, others through the precise alignment of the moon and stars. As of right now, however, I’ve only formed the spells for one such world. Can you think of it, Celestia? The new magic to discover, the knowledge we can attain!”
  “We?!” The princess approached him uneasily and countered, “I can’t just drop everything and go off to another dimension! I have a kingdom to run and protect, one that you appointed me to lead!”
  “Oh pish-posh! You say that as if the pursuit of knowledge isn’t a worthy goal.” His horn glowed, and the mirror came alive in a swirl of blue energy. “Besides, this will just be a quick test run. Just a simple look-see, and we’ll be back before you know it.” He gestured for her to follow and beckoned, “Come my friend. Adventure awaits!” 
  Without another word, the old wizard stepped through the portal, Celestia following uneasily. She emerged on the other side and shook herself, all four hooves landing on the ground as she asked, “And what has adventure…?”
  She and Star Swirl looked up, and up, and up, to find themselves gazing upon a large, scaly beast. It almost reminded them of a dragon, though it was without wings and far smaller than a full-grown drake. Nonetheless, their every instinct screamed the same thing as it turned its gaze upon them and its mouth opened to reveal several large, sharp teeth. 
  RUN.
  The creature let out a terrible roar just as they turned and went back the way they’d come, emerging back in Equestria none the worse for wear. Celestia looked to her old friend and asked, “Have you gone mad?! That thing could have eaten us!”
  “But it didn’t!” Star Swirl looked to his notes and reasoned, “Science is all about making little mistakes, after all. I’d best adjust the variables a bit, make certain the spells are pronounced correctly.” He turned back to her and noted, “I’d understand, of course, if you didn’t want to continue on.”
  The princess’ expression was fixed and neutral, but quickly turned to a mischievous smile that would one day have made Discord proud. “And miss out on the fun?”
  -
  “It looks like they visited a number of different worlds over the course of several decades.” By now, Twilight had a number of books gathered around her, each one filled with details about the various worlds Star Swirl and Celestia had visited. “That’s how Star Swirl was so magically advanced! He learned new things from other wizards as they explored, and recorded everything!”
  “Sounds kinda like cheatin’ on a test ta me, sugarcube.”
  “I admit, that does put it in a negative light, but a free exchange of ideas is necessary for scientific advancement. Besides, he did give credit where it was due, and that’s the important thing.” 
  “But Celestia never mentioned this to anyone? Not even Luna?”
  “There has to be a reason.” Her blank notebooks at the ready, she started using her magic to copy details and notations concerning the mirror’s construction and workings, as well as the assorted spells used to for travel between worlds. “Regardless, it looks like there was one world that they visited more often than the others, even until long after Luna’s banishment. Chances are that world is the one Celestia went to.” Her work on the original mirror concluded, she copied additional details on each of the intervening mirrors and continued, “But the research ends abruptly. There aren’t a lot of details about it beyond several incidents starting around the banishment and lasting several years. He started locking away the portals, the later ones first, and finished by sealing this one.” She groaned and added, “And there are pages missing! That just makes it worse!” 
  “Did someone come here and tear them out before we arrived?”
  “Or Star Swirl did it himself, for whatever reason.” Twilight groaned as she packed away the last of her materials and returned the books to their proper places. “In any case, we need to get to Princess Luna and let her know what we’ve learned.” 
  -
  A smile was clear on her face as Celestia emerged from the portal, one that soon faded as Star Swirl greeted her with a stern expression, the parchment with one particular coordinate spell etched upon it floating beside him. “Celestia. I would have words with you.” 
  “Ah. Well…”
  “How many times…” He gestured with one hoof to the parchment for emphasis. “…have you been here?”
  Like a frightened filly after having done something naughty and being found out, the princess shifted uneasily on her hooves and answered, “Not often…”
  “How often?!” The old wizard shouted, anger in his voice the likes of which she’d never heard before. 
  Celestia could barely look at him as she turned away and closed her eyes. “On and off, for a while.” 
  Star Swirl let out an enraged groan. “You know what kind of consequences there are to visiting this world too often! We’ve talked about this! You promised me…!” He took a quick breath to control himself before he continued. “We can’t risk it. You’re putting everypony in danger. What could possibly be worth something like that?”
  Tears were now flowing from her eyes as she looked up and asked, “What do you think is worth it?”
  Disappointment was clear upon his face as Star Swirl turned away and bowed his head. “No, Celestia. No.”
  “I’m sorry. But I can’t just…”
  “I’m ending this.” 
  Celestia’s gaze shot onto him as she asked, “What do you mean, ‘ending this’?! You can’t just…!”
  “I will not let you put your kingdom and his at risk. This is over. Now.” His horn glowed as he turned his gaze to the mirror and began chanting a spell. “Kingdom come and kingdom go…”
  As he chanted, Celestia cried out in protest, “No! Star Swirl, please! At least let me say goodbye!”
  “…Doth from this point, we close the door.” His spell was cast, and the journal at his side was closed and dropped to the ground with a thud. “I never want to talk about this again. I’m very disappointed in you, Princess.” He heard Celestia’s sobs as she turned and ran, the door to his study slamming shut behind her. He sighed and admitted, “I’m too old for this.”
  -
  “Night patrols are in, ma’am. Nothing to report.”
  “Very well, Sergeant. And our songbird?”
  The thestral looked uneasy as he admitted, “Looking up at the moon again, but no singing.” 
  Luna nodded. “Very well. You are dismissed.” The sergeant snapped off a salute, then turned and departed, leaving the princess and her companions be as she turned to Spike and explained, “A member of the regular forces has been spotted some nights looking up at the moon and singing softly. Sometimes one song, sometimes another.”
  “Anything special about the songs?”
  “Songs of love, of loss, of regret.” She waved a hoof and noted, “Should I ever see her, I will need to talk with her properly.” Her attention turned back to the door of the throne room as Twilight and the others arrived. “Princess Twilight, your timing is most fortuitous! What are the results of your labor?”
  “Very good! Let me explain!” She paused as she reached the throne, then amended, “Actually, it’s a lot to explain, so I’ll sum up instead. The mirror Celestia used was a prototype for the Crystal Mirror.”
  “This does not surprise me. Do continue.” 
  “But instead of being tied to just one world, it can go to a number of them, depending on the spell cast on the mirror!”
  “And this knowledge will allow us to locate my sister?”
  Twilight’s enthusiasm dipped as she explained, “The exact spell is missing, but with time…” A bright blue glow interrupted her as everyone present turned their gaze upon the mirror, a familiar form beginning to emerge. “Princess!”
  “Sister! Thank the maker!” Luna approached the mirror and continued, “Where have you been? I had no idea where you were or whether or not you would return! I do not appreciate…!” Luna’s complaints were interrupted as Celestia groaned in pain and collapsed before them, hardly looking like her usual, composed self. Her feathers were ruffled and crumbled, her peytral dented, one of her hoof-shoes missing, her crown damaged, and bruises present all over her body. In alarm, Luna rushed to her elder sibling and held her close. “Celie! What happened?!”
  Barely aware of her surroundings, the Princess of the Sun groaned two words before fading into unconsciousness. “Sombra…help…”
  Twilight and her gathered friends looked among one another in terror, then upon the mirror as the young alicorn asked, “Sombra? King Sombra?!”
to be continued...