"Huh," said Rainbow Dash.

"Huh?" Twilight glanced up from Daring Do and the Amethyst Eye, the autumn afternoon shade on this particular balcony of her palace just plain perfect for settling down and reading after what Rainbow called their 'weekly patrol.'

Yes, all they did was criss-cross the skies above Ponyville and the Everfree Forest for an hour or so every Thursday before stopping at Hayburger for lunch, but Rainbow insisted that these maneuvers were vital. "Rogue weather!" she would exclaim with a flaring of wings at least once during every patrol. "Lurking nests of changelings! Nightmare Moon cultists or Ahuizotl's henchponies! We've got a duty to protect Equestria from all that kinda stuff!"

And as much as Twilight agreed with those sentiments in principle, in practice, she mostly looked at it as an excuse to get out once a week and stretch her wings. The hour she then scheduled for her and Rainbow to geek out over Daring Do was an added bonus.

This time, though, Rainbow wasn't looking at her copy of the book. From her cushion by the balcony rail, she was looking down at the street that lead to the town square where the market was in full swing. "Whaddaya think about that?" she asked, nodding toward the crowd.

"'That'?" Blinking, Twilight stood and peered through the railing. Ponies moved along the road and among the stalls, the cinnamon-sweet scent of pumpkin bread and the salty-sweet scent of roasting peanuts drifting on the breeze, but as far as Twilight could tell, nothing but the usual buying, selling, talking, trading and laughing seemed to be going on. "What, exactly?"

With a sigh, Rainbow pointed a hoof. "That."

Twilight bent down, sighted along Rainbow's leg, and saw— "Rarity buying apples from Big McIntosh?" Straightening, she wrinkled her brow at Rainbow. "Why should I think anything about Rarity buying apples?"

Rainbow's mouth went sideways. "Maybe because she isn't buying apples."

Another blink, and Twilight squinted more intently, the Sweet Apple Acres booth sitting at the far end of the square. "Well, Rarity's got her saddlebags on, and whatever's in them is pushing out the sides in multiple rounded lumps, each of which is about the size of an apple." Shrugging, Twilight sat down and gave Rainbow a grin. "I think I'll stick with my original hypothesis, thank you."

"Really?" Eyes half-closed, Rainbow folded her front hooves. "So if she's buying apples, why are her saddlebags closed?"

"Because she's already bought them?" Twilight couldn't help turning it into a question. She knew from experience that Rainbow often picked up on things other ponies missed, but she also knew from experience how wild Rainbow's imagination could get.

"Exactly!" Rainbow leaped into a hover. "She's already bought them! Which means she's doing something else right now, doesn't it?"

"OK, fine." Twilight looked once more. "If you want to get technical, right now, she's talking to Big McIntosh."

"There it is!" Clapping her hooves together, Rainbow did a quick spin. "And why would Rarity be talking to Big Mac, huh? What could those two possibly have to talk about?"

Twilight tapped the balcony's crystal floor once for each reason: "The weather, the crops, the Ponytones' rehearsal schedule, how Applejack's doing, the latest Crusader escapade, the price of—"

"No, no, no!" Rainbow flopped back down onto her cushion. "Don't you get it? They've got a thing going on!"

"A thing?" And because it was Rainbow saying it instead of Rarity or even Fluttershy, Twilight decided she'd better make sure. "You mean a romantic thing?"

"Totally!" A sort of glow had come into Rainbow's eyes. "Like 'Beauty and the Beast,' y'know?"

Unable to stop herself, Twilight asked, "Which is which?"

Rainbow scowled. "This isn't a joke, Twi! Mac's obviously got it bad for Rarity, and there's no way she doesn't have it bad for him, too!"

Possibilities flashed through Twilight's mind. Could this be a changeling? Was Rainbow feverish with the feather flu? Had there been something suggestive in the book they'd been reading? But no: a changeling would know not to act so completely out-of-character; Rainbow had devoured two-and-a-half burgers and most of Twilight's fries at lunch; and Daring Do never did anything even remotely romantic in her books. That had always been one of the main attractions of the series in Twilight's mind, as a matter of fact.

But that meant, following Shamrock Homes's dictum, that since she'd eliminated the impossible, whatever remained, however improbable, had to be the truth.

"So, wait." For the first time in her life, Twilight found herself doubting something she'd read in the Great Detective's adventures. "You're telling me that you think Rarity and Big McIntosh—"

"Oh, they'd never admit it!" Rainbow waved a hoof. "But look at them!"

Twilight's gaze slid unwillingly to the scene again, and she did a double-take. Rarity and Mac continued facing each other as they had been for some minutes now. "They're still talking?" She couldn't stop a gasp.

"Yep, yep, yep." Rainbow polished a front hoof against her chest. "Did I call it, or did I call it?"

"There—" Every thought seemed to desert Twilight. "There's got to be some other explanation!"

"Trust me, Twi." Rainbow touched the side of her nose. "I know all about this stuff."

"You?"

Rainbow narrowed her eyes. "And whaddaya mean by that?"

"Well?" All Twilight could do was flail her hooves. "The only thing I've ever heard you say about romance is that it's stupid and mushy! Am I suddenly supposed to accept that you've now become some sort of expert on the subject?"

Clearing her throat, Rainbow gave a sniff. "A real lady don't kiss and tell, all right?" That glow seemed to come over her again, and she hunched forward on her cushion. "The important thing is that we hafta help 'em get together. 'Cause that's what friends do for their friends, right?"

"I...guess..." Head still spinning, Twilight moved her stare back and forth between Rainbow and the two—still talking!—out in town square. "But this is more Cadance's field, don't you think? I mean, if they're really—" She stopped, unable to make herself say it. Could one of her friends truly be in love?

"Cadance?" Rainbow blew a noisy breath through her lips. "No way! This is Applejack's brother and Rarity we're talking about! If we can't handle this, nopony can!" She jumped up and began pacing along the balcony. "We'll need Applejack to talk to Big Mac, of course, and Fluttershy to handle Rarity, so—"

"What?" Twilight fought the urge to grab Rainbow and shake her. "We don't even know for sure that anything's going on!"

Rainbow stopped. Her left eyebrow arched, and she gestured to the view past the balcony rail.

Almost afraid to look, Twilight glanced down to see Rarity laughing at something Big McIntosh had just said. Then Rarity leaned forward, and Big Mac began laughing.

"Unless..." A quizzical note came into Rainbow's voice. "Are you getting weird 'cause you like Big Mac?"

"Me?" Just the idea stole Twilight's voice for a moment. "No!"

"Good." Rainbow gave a sly grin. "Since you already got a coltfriend up north and all."

"He's not—! I don't—! We've never even really talked, and there isn't—!" Biting off her further objections, Twilight tried to ignore the warmth spreading across her face and pushed on. "Look, Rainbow, you said it yourself: this isn't a joke or a game or anything like that. If you're right, then this is something real and adult, and we've got to take it seriously!"

"Adult?" With another clearing of her throat, Rainbow leaned against the railing. "Says Princess Twilight from the balcony of the castle she got after saving the world for, like, the third or fourth time."

Scowling, Twilight waved a hoof. "OK, yes, fine. But having a job and responsibilities and everything, that's just a matter of applying knowledge and honing skills. Love is—" She shook her head and presented the conclusion she'd come to after studying numerous novels and non-fiction works on this very subject. "Saving the world is a sprint: a big effort, sure, but it's quick and one-time. You leap into it, and you either succeed or you fail. Love is a marathon: a long-term commitment that you nurture and develop every minute of every hour of every day. And if it falls apart, you don't get snuffed out like a candle like you might with the world-saving thing. No, you've still got to go on living no matter how painful and terrible it might be."

She swallowed, her heart thud-thud-thudding in her ears. "Being a princess is hard, but when you get right down to it, I've been training for it my whole life. But being in love?" The breath she took went in shaky, and she blew it out hard in an attempt to steady herself. "That's something to be very, very careful about."

Rainbow clicked her tongue. "Don't date much, do you?"

Twilight clenched her teeth. "Rainbow!"

"Okay, okay." Sitting down, Rainbow spread her front hooves. "I'll admit that you're maybe kinda right about some of that. 'Cause, sure, nothing's worse than love gone wrong." A smile touched her snout, a smile about as gentle as any Twilight had ever seen from her friend. "But when it goes right, there's nothing better. And if we can help things go right with Rarity and Big Mac, then we've got to. That's what I'm saying."

Unable to stop herself, Twilight glanced through the railing again. Rarity was just now walking away from the Sweet Apple Acres cart, both her smile and Big Mac's easily visible even from this distance. "We'll be careful?" she heard herself ask.

"Of course!" A whoosh, and Rainbow slid up beside her, one front leg hooking around her shoulders. "I mean, c'mon! When aren't we?"