I did have to look up the "seven" for trilogy. Heptalogy is the word for a series of 7 books. Like Harry Potter for example. So this would be a series of 7 stories.

Chapter 1: Twilight Sparkle's Day

It was 7:00AM; Twilight awoke to the sound of her alarm clock. She knew what day it was today, she had marked down in her calendar that it was Applebloom's birthday. It was something that all of her friends were being invited to. Twilight continued to brush her mane using her magic when a letter hit her on the back of the head. She bent over to it, and using her magic started to read:

Dear Twilight Sparkle.

I have a new friendship assignment for you and your friends. Please come to Canterlot immediately to receive this assignment.

Yours Sincerely:

Princess Celestia.

"A new friendship lesson from Princess Celestia?" she asked herself before squealing. "This is very exciting! I must find my friends and tell them about it so we can go together!"

Twilight put her brush down on the bathroom bench and started to head out the door, when a familiar purple claw stopped her from going any further.

"Twilight? Where are you going?" Spike the little dragon asked.

"I have a new friendship assignment from Princess Celestia. I have to find my friends so we can go and see what it is"

"Even Starlight Glimmer? I'm pretty sure she's still in the castle"

"Perfect! She can help me look for them!"

Alas, Spike was wrong. Twilight looked in Starlight's room but she wasn't there.

"Where is she?" Twilight asked.

"I don't know. Last time I saw her she was here. She said something about a mysterious cave that she and Trixie were going to check out and-"

"And she didn't use the door?" Twilight interrupted.

"Twilight, she's a powerful unicorn. Odds are she probably teleported"

"Worry about her later, I'm going to search for everyone else. If I know correctly, they should be preparing for Applebloom's birthday party"

Twilight started her search. The first pony that came to mind was Applejack. She ran over to Sweet Apple Acres where an anxious Applebloom stood waiting.

"Applebloom, thank goodness!" Twilight puffed. "Have you seen your sister around?"

"Actually, you just missed her" the yellow filly replied.

Twilight's ears dropped.

"Where in Equestria did she go?"

"She didn't say. It was so strange. After Granny Smith mentioned about how many presents I would receive, Applejack just burst out the door with no explanation"

"Ugh, but I had something really important to tell her!"

"Maybe you should've come earlier then"

Twilight proceeded to run out of Sweet Apple Acres, not quite satisfied with the result she got. She ran all the way to Ponyville Square until she thought of the next pony she could find.

"If I can't find Starlight Glimmer or Applejack, no matter; five ponies including myself will still be enough. I'll just find Pinkie Pie. She should be easy; she's baking a cake for Applebloom's birthday"

Twilight ran to Sugarcube Corner where they saw the cakes hard at work making other food for the parties. But she didn't see Pinkie Pie. She wasn't even playing with Pound and Pumpkin Cake.

"Excuse me, do you know where Pinkie Pie is?" a stressed Twilight asked them.

"Well, she was busy making a cake. Then we smelt something off in the oven when she rushed out, with no explanation" Mrs. Cake replied.

'Hmm, that seems very familiar to what Applebloom said about Applejack. She also said 'with no explanation'' Twilight thought.

"So, she didn't tell you where she was going?" Twilight asked again.

"I'm afraid not"

"Well, thanks again!"

Twilight ran into the center of town again. She was very distraught when she surprisingly bumped into Fluttershy.

"Twilight, I'm so sorry!" Fluttershy apologized.

"Finally, I've found one of my friends!" Twilight exclaimed.

"What are you talking about?" Fluttershy asked.

"Do you know where Applejack or Pinkie Pie are?"

"No, I haven't seen them" Fluttershy replied. "I thought they were busy preparing for Applebloom's birthday party"

"I checked those places; both Sweet Apple Acres and Sugarcube Corner, but they weren't there!"

"Oh my. That is awfully bizarre"

"But since I've found you, do you mind coming with me? There's something important we have to do"

"Oh Twilight, I wish I could, but I'm in a rush to get somewhere and I'm already late. Maybe later?"

Twilight sighed.

"Fine, I'll let you go. It sounds like what you have is more important anyway"

Fluttershy sped out of her reach, which was very unusual. Twilight shrugged and kept moving.

"With Starlight Glimmer, Applejack, Pinkie Pie and Fluttershy out of the picture; it's just Rarity and Rainbow Dash that I have to find" Twilight said to herself, arriving at Carousel Boutique. "Rarity should be here. She would never get distracted when making a dress"

Twilight knocked on the door. No reply. She flew up to her working area, there wasn't anypony there. All she saw was her cat. Twilight broke through the window and grabbed opal, who was not very happy to be grabbed.

"Opal, I think your name is. Can you tell me where Rarity is?"

The white cat gave no response as she scratched Twilight on her cheek. Twilight dropped the cat and cradled her cheek in pain.

"Thanks anyway!" she said. "Ow. That is the last time I try to handle Rarity's cat"

She grabbed some bandages from her bag and wrapped them around her cheek.

"Rarity is gone too, I guess Rainbow Dash is the only one I have to find" Twilight sighed. She flew up to Rainbow's house and knocked. No surprise, Rainbow Dash was nowhere to be found. She didn't even leave a note. But there was something that she did see at the bottom of the cloudominium, she saw a burnt cake. It was hardened and had black chars all over it. It was also covered with grass and mud. She flew to the cake with curiosity.

"Who would throw a cake at Rainbow Dash's house?" she asked herself. But she had other things to worry about. Princess Celestia was probably going to be mad at her for not arriving.

"After all this searching, none of my friends could come with me?!" she asked again, frustrated. "What could they be possibly doing that is more important?"

Next Chapter: Applejack's Day (29/12/16)

I uploaded this at 8:30AM on the 28th of December in my Time Zone (UTC + 10:00). So it would be different depending on where in the world the reader is.