"Happy Birthday, Princess Celestia!" Pinkie Pie shouted as she threw an armful of confetti into the air.

On the train seat in front of her, Rainbow Dash jumped in shock, her wings flaring. "Pinkie!" she said, turning around to glare at the earth pony. "What are you doing? We're not even to Canterlot yet!"

Pinkie Pie laughed. "I know," she said. "I'm practicing for when we actually celebrate Princess Celestia's birthday! Do you think I should add balloons? Streamers?" She clopped her hooves together anxiously. "Oh man, how the cupcake am I gonna properly wish happy birthday to the supreme ruler of all Equestria?!"

Across the aisle, Twilight Sparkle chuckled. "Don't worry about it, Pinkie," the purple alicorn said. "I don't think Princess Celestia is expecting a mind-blowing celebration. The invitation I got seemed pretty low-key." She magically levitated the scroll containing the invitation and scanned it again. It looked nothing like the fancy invitations for the Grand Galloping Gala. It was more of a simple note requesting the presence of Twilight and her friends at Celestia's birthday luncheon.

"Oh, but darling!" Rarity said from the seat behind her. "One simply must celebrate a royal birthday in grand fashion! After all, this is our dear Princess of Equestria we're talking about!"

Next to Twilight, Starlight Glimmer poked her chin with her hoof. "Come to think of it," the unicorn said, "I don't recall Celestia ever making a big deal about her birthday. All I ever heard about when I was a filly was the Summer Sun Celebration. Twilight, was it any different in Canterlot?"

"No," Twilight said, shaking her head. She smiled. "Although when I was her pupil, Celestia did take me out for lunch on my birthday every year. And she always bought me a book or two." That alicorn really did know how to make everypony feel special, Twilight thought.

"That was sure nice of her," Fluttershy said. "Maybe the princess just doesn't like drawing attention to herself. I know what that's like."

Rarity tossed her mane. "Well, I, for one, shall make sure the princess has a delightful birthday! She was kind enough to invite us all to Canterlot to celebrate with her, and I am going to be a gracious guest."

Meanwhile, Spike munched on an apple fritter from the supply of snacks Applejack had brought. "It is kinda weird, though," he said. "I mean, she and Princess Luna go all-out for the Summer Sun Celebration."

"Celestia told me a little more about the Summer Sun Celebration a while back," Twilight Sparkle said to her dragon companion. "It was never her idea to begin with. The other ponies started it when they learned that she had defeated Nightmare Moon. Celestia actually wanted to make it a day of observance to honor all of the good her sister had done in the past, but everypony else just wanted to commemorate Nightmare Moon's banishment."

"I'm glad both she and Luna participate in the Celebration now," Fluttershy said. "Luna deserves to feel special, too. I think Celestia's just glad her sister is back."

"I think so, too," Starlight said. She glanced out the window. "Oh! There's Canterlot, up ahead!"

Pinkie Pie let out a dramatic gasp. "Oh no!" she said. "I don't have much time! I have to decide what kind of balloons to inflate! Rainbow Dash, help me out here!" She flung a pile of still-deflated balloons at the pegasus, and Rainbow sighed.

As the train pulled away from Canterlot Station, the girls and Spike checked their luggage to make sure nothing had been forgotten. "Looks like everything's here," Applejack said, leaning against the pile of suitcases. "Includin' Rarity's entire ensemble."

"Excuse me!" Rarity said. "At least two of those bags are some of my latest designs that I'm putting up for sale at Canterlot Boutique! Might as well take care of some business matters while I'm here, after all."

"Wasn't Celestia supposed to meet us here?" Spike asked, looking around the station platform.

"Something probably came up," Twilight said. "You know how busy she is—oh, there's Princess Luna!" She pointed a hoof at the midnight-blue alicorn who had just touched down on the platform.

"Hi, Princess Luna!" Pinkie Pie said. "Don't worry! I haven't forgotten about your birthday! It's in 243 days—hey, why is your smile on vacation?"

Indeed, Luna's expression was serious as she approached the other ponies. "Twilight Sparkle and friends," she said gravely. "I'm glad you could make it."

"Have you been taking lessons from Pinkie's sister Maud?" Rainbow Dash asked. "Or do you just hate birthdays that much?"

Twilight Sparkle shot her an annoyed glance. "Luna, what's wrong?" Twilight asked, her ears drooping. All sorts of worries filled her head and a knot formed in her stomach. This was not at all what she had been expecting.

Luna paused and looked around. "Perhaps it's best if you see for yourself," she said in a low voice. "Let's get back to the palace."

As their carriage bounced through the streets of Canterlot, Twilight looked out at the busy ponies. Everything seemed normal. And whatever was going on, Luna didn't want to discuss it in public. Twilight only hoped Celestia was okay.

When they reached the palace, Luna led their guests to Celestia's chambers. She paused in front of a door and then magically opened it, and Twilight clopped inside.

Celestia lay in her bed, her legs tucked against her body and her eyes clenched shut. Her hooves twitched like she was dreaming about something, and the expression on her face was pained.

Twilight's breath caught in her throat. "What happened?" she asked Luna. "Is she sick?"

"I don't know," Luna said. "She's been acting odd for the past week—lethargic and anxious. This morning, she seemed like she barely had enough energy to raise the sun, and then she went back to bed. She told me she would meet me at breakfast, but she never did… and then I found her like this."

"Is she dreaming?" Starlight asked. "Can't you go into her dreams and see what's going on?"

"I tried," Luna said. "Something is blocking me from accessing her dreams. It's some sort of magic that I'm not familiar with."

Rainbow Dash stomped the floor. "Aww man, who would do this to the princess?" she asked. "When I find 'em, I'm gonna throw 'em in the dungeon and have a dragon eat the key!"

"I hope that dragon isn't me," Spike said. "I've eaten keys before. Too much metal." He stuck out his tongue in disgust.

"What do we do?" Twilight asked, pacing around Celestia's bed. She reached out a hoof to the white alicorn's shoulder. Suddenly a ripple of dark magic jolted out of Celestia, flinging Twilight away. She spread her wings and righted herself, so her fall turned into more of a stumble.

Luna's turquoise eyes narrowed. "What sort of foul magic is this? How dare somepony do this to my sister?!" She reared up, her horn flaring with magic that streamed toward the sun-alicorn. Again the dark magic manifested in thick tendrils that pushed Luna's energy away.

Gritting her teeth, Twilight leaped over to the alicorn's side, horn aglow. A surge of her power merged with Luna's own magic and bore down on Celestia, causing the dark barrier to strain under its might. Twilight dug her hooves into the rug and willed forth more power.

Then their magic snapped and its dissonance rang through Twilight's body. She and Luna cried out and staggered back, reeling from the psychic blow, as the dark magic swirled around Celestia before retreating back into the white alicorn's head.

Starlight reached out and caught Twilight, who held her face in her hoof as she moaned in pain. "Twilight—what kind of magic is that?" the unicorn asked. "And how is it resisting both you and Luna?"

Luna shook her mane, wincing. "That is a terribly powerful spell," she breathed. "Something filled with immense sorrow and fear. I've never seen anything like it."

"Neither have I," Twilight admitted. "Is that what that horrible feeling was? Sorrow and fear?" It did feel like the magic was laced with misery, like the worst day Twilight had ever had, or all of the times things had gone wrong in Equestria.

Luna nodded slowly, then turned to watch the pained breathing of her sister, her own eyes wide and her ears turned down.

"Well, that's just plain awful!" Pinkie Pie said. She bounced up to the alicorns. "I know what Princess Celestia needs! She needs the happiest, most fun birthday party ever! And I've got just the party cannon to wake her up from that funk!" The earth pony reached into her tail.

Applejack put out a hoof to stop her. "Not right now, Pinkie," she said. "This ain't no time for a party."

Luna blinked and turned back toward the other ponies. "Wait—yes, that's it! Happiness! She needs happiness!"

"Told ya!" Pinkie said, reaching back into her tail.

"I'm afraid your party supplies won't be enough, Pinkie Pie," Luna said. "She needs happiness magic."

"Happiness magic?" Twilight asked. "I'm on it! I'll go straight to the library and brush up on my emotion spells! C'mon, Starlight!"

"Wait, Twilight Sparkle!" Luna said. Spreading her wings, the midnight blue alicorn soared over their heads and cut them off at the door. "I have a different task for you this day. You must bring Princess Radiant Dawn to Canterlot."